to gut load mealworms, keep them in grain (wheatbran, rolled oaks etc). Carrots and wholesome greens (collards, dandelion etc) can be placed onto of the grains and the mealworms (superworms can be offered the same as well) will eat it. Just make sure to wash the vegetables and greens and pat dry as you don't want to get the grain too wet as it can mold. Another thing you can do is add a pinch of calcium and multivitamin powder into the grains. Not sure if any of this would be absorbed by the mealworms, but certainly can't hurt.
All insects should be fed at least 24 hours before giving them to your reptiles. Crickets can be fed the same greens mentioned above, as well as Kale, mustard/turnup greens, endive and escaroli, bell peppers, carrots etc. Pretty much the same sort of greens you would feed a green iguana or bearded dragon. Moisture can be given via a slice of orange, potatoe, carrot or squash.
Silkworms should be fed silkworm chow (comes in a powdered form which is mixed in water and cooked in the microwave for about 5-6 minutes) or freshly washed mulberry tree leaves.
Waxworms I beleive they need to be fed bran mixed with honey, but not hundred percent sure with these.