You might have an easier time finding that in a market, or corner store, than a supermarket, but you might not find everything you are looking for, and it might all be a bit more expensive than a supermarket. Depending on how many placed you go to show (taking more time), buying smaller portions at smaller stores may end up taking more time and cost close to the same amount as the larger portion. There's not a lot of incentive in that besides not being wasteful.

Also, you're probably unlikely to find much measured to 100 or 200 grams in any US supermarket. It's all ounces (both fluid and otherwise!) here. ;)

I've never seen half dozen egg cartons or single sticks of butter sold in supermarkets, but my experience is somewhat limited. Eggs and butter last for a while so I don't think this is really a big deal. And you can generally get as much meat as you want in the deli/butcher section of a supermarket.

Yes, OP does not relate to my experiences at all. If there is one thing the US has no issues in it is consumer choice / variety. The only thing frustrating about grocery shopping for me is that I have to do it so often since I go through my ingredients so quickly.