Like Peter Crabtree has already said this is a very subjective question and each will have his own take on it. During the 1970's when match fishing the Trent I only ever used caster and hemp. My mate and I would take off around two gallon a week for our own use. The key to keeping them fresh, as opposed to just keeping them, is temperature. Kept in a sealed bag or bait tin, fridged at setting 3 or 4, I would be happy to use them up to five days. Keeping them in water is OK, up to a point, they certainly won't float because they are dead (drowned) and therefore will quickly begin to deteriorate. They will still have limited use, chub and carp love them but roach and bream aren't so keen once they have gone "off". The best thing to do is to buy just enough for your immediate use and don't keep them for more than three days. However to put it in prospective I remember fishing the River Derwent at Sawley many years ago and running out of maggots. I got through a gallon in 6 hours and taken around 80 to 90 lb of fish. The only bait I had left was two pints of casters in sealed bags that had been in the bottom of my box for weeks. They were black and to say they were rancid was complementary. I fed a handful in and the water erupted with chub. I carried on to take another twenty odd pound, never caught a roach on them through. So there are two sides of the coin to chew on. My personal preference is to try and use the freshest bait I can. But it is a fact that if the fish want old bait they will take it, you see that's fishing, nothing is consistent, thank the Gods. Pete.