3D Printers/Microforges are reasonably common now. Artemis has one and some of the people in town have one. These can print pretty much any non-organic material one wants, given the size limitations of the particular forge, as long as the user has the program and the necessary raw materials.
This creates two bottlenecks: the programs themselves, and rare raw materials. Iron is easy--the trace elements in some types of steel, or the trace elements in microchips? Harder to find.
We haven't yet established how recycling old scavenged materials will work, but it probably does with some losses.
Artemis has a very extensive cache of rare elements and other supplies. This is what the raiders are after in the first book.
- Biologicals will boom by 2054. Notably vats growing algae will allow a lot of materials to be created, including petrochemicals and spider silk. These vats can be housed in garages with the right starting materials. The right algae could synthesize gasoline.
The issue with 3D printers will be the draw stock. For metal you'll need the ability to manufacture alloy wire. For plastics, you'll need the ability to create beads and the materials science knowledge for distinguishing formulations.
Recycling metals is dead easy. All you need is heat and some minerals like borax, etc. and a basic knowledge of how to identify common alloys. Smelting from scratch is a bit more difficult, as you need other things (chromium for stainless, manganese for spring, etc.) on hand, but most of those things are get-able if you know where to look (certainly recoverable from old existing materials, and still pretty get-able from the ground in the continental US) Anyone who has a smithee has everything they need to smelt. Limiting factors are fuel (you'll need a charcoal maker if you don't have access to coal, or people will have to make their own - either way, there is logging necessary)
Recycling plastics into reusable virgin stock harder--much more energy intensive - but a little handwavium could get you bio-engineered algae that can do part of the work for you. OTOH, re-purposing plastics (making countertops, handles, utensils, etc. out of old bottles, for example) is simple enough that anyone with a crucible can do it in their garage.
Reusing metals is also dead easy as long as you have power. Without power, it becomes much more difficult, but certainly not impossible. The key to your manufacturing is going to be electricity and machine tools (which can be manufactured from scrap to pretty fine tolerances, and which self-bootstrap if the operator knows what he's doing) and (the most difficult part) lubricants. This latter will be the real bottleneck - if you can't get petroleum, it'll have to be whale oil, and that means a lot of whaling and some trade routes...or some custom biotech (again, not outside the realm of realism).
The biggest elephant in the room is electronics. Electronics are *tough* and depend on supply chains that are not easily re-assembled or re-created on a small scale (not to say it can't be done, but it's a huge ask both in terms of chemistry and in terms of precision equipment). The abundance of salvagable electronics parts (even in a Carrington event) for re-purposing actually woks against the continuing existence of electronics in your world, since the more there is to salvage, the less demand there is for new stuff, and once that supply chain has a hard break you've got a much harder job putting it back together than you do maintaining it. Now, that said, old-style electronics (vacuum-tube era) is something you can do in any glass-blowing shop or smithee, so all you'd need for that is some books. That gives you pretty easy access to rudimentary radio and calculation, and probably a lot more now that more is known about how electronics function and what they can do, but the available cycles will be quite thin. Even if they have no moving parts, electronics eventually die due to chemical interactions inside of transistors, MOSFETS, ICs, etc. eventually breaking and corroding signal pathways--in your world, working electronics are the new gold (though not as permanent).
This has some pretty big implications for your two baseline technical assumptions: Solar power and 3D printing. Neither works without complex electronics, so the moment your die-off happens, both technological suites are on a death-clock. Your characters will need to use the leeway they provide to either rebuild electronics manufacturing capabilities and supply chains for raw materials, or they need to have a plan for moving OFF of these technologies and be working towards it (even if they are simultaneously doing their best to expand their time horizon with aggressive salvage operations - which, btw, will be so important to any survivors that good salvage will be the resource over which wars are fought).
In solar power the electronics are in the inverters and charge controllers. Any new battery tech will be *heavily* dependent on this. Old battery tech (like the Nickel-Iron Edison battery) not so much, but the maintenance on those things is a big deal. Solar panels also decay due to weathering - though this theoretically might be delayed/offset if you have someone in town who polishes glass and makes a rig that can polish the glass to instrument-quality clarity. AC/DC inversion can be done at a macro scale, so inverters could theoretically be rebuilt to supply household voltage - or everything could just be rewired to go DC and eliminate the need for inverters. You'll still need transformers to control voltage/amperage delivery, but, again, these can be built without complex supply chains (epoxies would have to be worked around, but it is do-able).
Modular nuclear would be a real coup--if your world has these things then your community has a 30yr time horizon before fuel or maintenance becomes a problem (assuming no sabotage or other catastrophic failure).
In any of these cases, you're going to need to factor in grid maintenance, which is non-trivial and, again, is supply-chain dependent at a number of levels. I can get into that if you want me to.
However, there are viable and renewable alternatives. Wind, microhydro, biotech, and wood gassification can do a lot, and could stretch your civilizational lifetime out a century, which oughta be enough for a good solid reboot to happen.
- We talked a lot about wind and micro hydro as viable energy sources, especially if the town grid was small and/or homesteads were off the grid. Micro hydro can be built out of an old washing machine.
- Additionally, while we tend to think of electricity as vital, a lot of machines historically ran without it. For example, pumps and many machine tools. Consider what the Amish are able to make.
- Old fashioned machine tools like lathes are much more capable than we think of today. The Revolutionary War demonstrated one could make high quality rifles with tight tolerances on standard wood lathes. There's a lot the folks in town could do by rediscovering these non-electric machine shop technologies.
- This makes it possible to reserve electricity for the stuff that really needs it. The town would've found ways to get as much work done without electricity as possible.
- A great deal of electronics components would be salvageable. Some, like circuit boards, can be etched instead of printed. Also, older electronics can be formulated chemically.
- Old army manuals would have a lot of "how to" with lower tech directions.