gut loading?

What do you feed crickets to make sure they are gut loaded?? I have bearded dragons on the way and bought 200 crickets and wanted to know what to feed them to gut load them

I use to give crickets the same thing I give to my dubia. Fruits, veggies (carrots, greens esp), and cat food. They sell premade guy load at the pet store that I used a lot. It looks like wet, orange squares in a jar.

Thank you