What are some good side gigs for some extra cash that an active duty soldier could get into easily?

I’ve seen a ton of service members doing Lyft and Uber

Lots. I am a delivery driver for Dominos as well as a photographer.

Common is usually pizza delivery driver. They tend to be flexible and appreciate having someone who can deliver on post without issues. As long as you have the approval of the chain of command and it doesn't interfere with your duties. One of my soldiers a while back would pull in 50-200 in tips a weekend depending on the usual ebb and flow of sporting events, etc.