i have scoured my house and garage to find good reliable cache containers, and here is what I have found.
lock & locks
pill holders
match containers (I replace the o-ring with something a little beefier)
and the one that no one else said yet,,, valspar paint sample containers! They are $3, and have a gasket seal and are a good size with a large lid.
Another thing, keep the lids from things like cleaning supplies and drink bottles,(anything that has a gasket under the cap) You never know when you will find a container that they will fit and will then make a good waterproof cache container. For example,the jar from generic zantac from walmart isn't waterproof, but if you take the lid from a large jug of pinesol, it makes a good micro. just be sure to clean everything!