Welcome to H4O from So Cal, (not the same SC).
I always say that the first thing to get before you go off road is AAA premier membership. The premier membership includes unlimited towing, but you have to have your membership for 1 year without using the towing service before you can upgrade to premier. If you're careful you won't need it, but if you screw up off road, a couple hundred mile tow bill can add to the pain of getting it repaired.
There is lots of great advice on here regarding modifications to make you're Hummers more capable, but for easy to moderate trails, Hummers are ready to go right off the show room floor. You only need mods if push the limits.
Nice looking H's you got there. How are yours equipped? Is the H3 a base model, adventure or luxury? Mine is a luxury model (i.e. heated leather seats) with the off road package (lockers front and rear).