Hey Jude,

You're absolutely right in that you need both a moisture source and a dry feed source. Acceptable moisture sources that can double up in gutloading benefits include salad items like darky leafy greens, veggies, and various fruits. Be cautious using items that are extremely damp or that won't be eaten within 24-36 hours as mold can begin to flourish. Dry feed/gutload items were discussed pretty thoroughly in this thread by Lynn. I'm sure whatever you are buying online is a perfectly fine gutload, just read the ingrediant list and look for quality ingrediants and little to no BS additives. I personally use ground mixes of non-medicated chick starter, quality dog and cat kibble, fish food, and a few additional addititves for select feeders like spirulina algae and bee pollen.

As for the water crystals - I prefer them for roaches because their moisture demands are actually quite high (particularly for wing biting and cannibalistic species). They're a nice items to have on hand because they are extremely cheap and make for a nice constant hydration supply to feeders to be used at all times. They do a pretty good job at resisting mold, but when dealing with crickets who tend to be a little "filthier" you will want to replace moisture sources every couple of days to prevent bacterial manifestation. These are also fine to feed mealworms and zophobas if you can avoid direct substrate content.

You can get water crystals from a number of suppliers, a couple off the top of my head are Aaron Pauling and Greg's Exotic Inverts:
Aaron Pauling.com
Greg's Exotic Inverts Home - Greg's Exotic Inverts <-- Lower Price

Most roach suppliers sell water crystals, and they are becoming a more popular item at shows and by private sellers on classifieds or other feeder sites. Hard to beat a buck (or less) per gallon of gel! Effortless to make, just add water and let them sit for a few hours! Hope this helps some = )