Nice, I never thought of that, but that would probably be too hot for the summer time (unless you actually WERE swimming). For me, I use a traditional binder, but if I am really active (roller skating, running) then I wear a sports bra with a few extra layers. I'm glad I have smaller breasts.
I've used a neoprene waist shaper before. Too sweaty. Found a waist shaper made of breathable material on Ebay so I use that. It does up with little hooks at the front, but it's undetectable under clothing.
When I was a young teen, I made my own that was basically just a strip of fabric with a zipper connecting it into a tube shape. It worked for years, thankfully I got an underworks one later on. I hated that binder though, it was so thick and hot and uncomfortable, I have a small chest and it had a LOT more binding power than I needed.
I used duct tape to just pull my breasts to the side at a party one night so I could be shirtless haha, I was among friends and it was all good, I only had it on for a few hours. Hurts like a bitch to remove, I can't imagine how bad it would be to wear all day D;
I can't think of anything else really. I've had a proper binder since high school and haven't needed to use anything other than that.
One of my first experiments with binding involved taking a pair of control-top panty hose and cutting most of the legs off to put my arms through and cutting a hole in the crotch to put my head through. Hot, awkward, and not entirely effective. Oh, the wonders of advice you get on the internet...