America isn't the bargain paradise that it used to be. You can get camera stuff here for more or less the same price online, so taking in to account any warranty issues and potential duty/vat payments [and note the "potential"], then unless you find a sale or clearance bargain there's not much to be had. That's not to say that you shouldn't look anyway and buy something you fancy or haven't seen over here on impulse. That's the fun of being on holiday.
As for other stuff, I love going in to the DIY warehouses - Home Depot, Lowes etc. Twice the size or more than our own and I usually pick up all manner of odds and ends and knick knacks. Plus it's interesting looking at the bigger household and gardening stuff. The tools/diy section of Sears is interesting. Good quality tools at a good price - Craftsman, plus all manner of useful bits. Also have a look at the bigger stuff - TVs, kitchen appliances etc, and see what they pay compared to us.
I always find bits and pieces in Walmart, K Mart and Target as well. Nothing essential but things that "come in useful", and cheap.