What I feed mine is Hikari First Bites, PhytoPlan by Two Little Fishies, which is basically phytoplankton, a natural source of food for bamboo shrimp. You can also feed them ZoPlan which is zooplankton, also a natural source of food for these guys. Dr Foster and Smith carries both.
Tetramin tropical tablets also work. They are sinking tablets that look like aspirin and are cheaper than the foods mentioned above. You would have to use a shotglass with a little water in it though to get them to soften up and break down into powder.
Ever since I've started using these foods, my bamboo shrimp have stopped scavanging the substrate [when they do that it means means they're starving and it's somewhat stressful for them]. Only times I see them do that is when I neglect feeding them. With a fairly aged aquarium, I don't have to spot-feed that often, maybe 3 times a week.
I prefer letting the food float instead of wetting it. What I do is drop a small pinch of either First Bites or PhytoPlan. This floats on the surface and the filter current [which is a standard Tetra Whisper PF-10i] draws it to the outlet and the current takes it to the bamboos. Another thing I have done in the past is drop a quarter of a tetramin tropical tablet right between the chemical and biological filters. The current is strong there and the piece slowly breaks down and the bits and pieces get into the water column. Not sure how effective this is but by my reasoning, works pretty well. Whatever is left gets picked up by my clean-up crew which consists of a hoard of malaysian trumpet snails and ghost shrimp. BTW, the ghost shrimp go CRAZY when they sense the phytoplankton. They seem to really, I mean REALLY like it. Alas, they have a hard time feeding on it from what I can tell because it is a VERY fine type of food, almost like dust.
So there you have it. Any other suggestions are more than welcome as I'm no expert at this, I just stated what I'm doing and what seems to work for me