An awful lot of stuff. I wouldn't even know where to begin, especially if you're willing to consider a hybrid model where some parts / sub-assemblies are manufactured elsewhere and delivered to you (for example, having PCB's produced by OSHpark or PCBway, etc.) and you do final assembly in the garage.
If it were me, I'd also be looking at scenarios that involve any kind of "thing" that I could acquire cheaply and re-purpose somehow. Making lamps out of old wine bottles, that sort of thing.
Robots, unmanned vehicles of various sorts, all sorts of small electronic gadgets, probably some auto accessories... really, the range of things you could (at least hypothetically) manufacture in a space that size is huge.
Now whether or not you could manufacture the thing at scale may be a different question. You could probably easily accommodate doing something the size of a small home appliance (think: washing machine size) if you only had to do one at a time. But doing that at scale might well require more space. So is the intent to stay in the garage and run an enduring business there, or just to ship a prototype, prove the model, and then maybe expand? Or is this purely an academic thought experiment?
I’m doing something very much like what you describe. Small footprint IoT device, we get the custom designed PCB’s shipped in and most of our BoM is generic off the shelf stuff that is already available on Alibaba/AliExpress. Our enclosure and other plastics are designed in house and injection molded in my two car garage with molds printed on a resin printer. Soldering is custom ordered overseas where possible and hand soldered when not.
The Buster Beagle was a real game changer in this space, though if your parts are really small there are other even cheaper options.
The goal is to, as you say, prove the prototype and then get a larger dedicated space. The product I have is not super niche and could theoretically grow a lot, but we are planning to be pretty adaptable by focusing a lot on COTS components, the kind that you can go onto Alibaba and find 5 factories for whatever you need.
If it were me, I'd also be looking at scenarios that involve any kind of "thing" that I could acquire cheaply and re-purpose somehow. Making lamps out of old wine bottles, that sort of thing.
Robots, unmanned vehicles of various sorts, all sorts of small electronic gadgets, probably some auto accessories... really, the range of things you could (at least hypothetically) manufacture in a space that size is huge.
Now whether or not you could manufacture the thing at scale may be a different question. You could probably easily accommodate doing something the size of a small home appliance (think: washing machine size) if you only had to do one at a time. But doing that at scale might well require more space. So is the intent to stay in the garage and run an enduring business there, or just to ship a prototype, prove the model, and then maybe expand? Or is this purely an academic thought experiment?