I managed the units I worked with back when the USO did long tours years ago... when they paid entertainers....not a lot, but we took entertainment from home to a lot of places where there wasn't much entertainment. One tour took me to the top of Mt. Suribachi on Iwo Jima, a place I would never have seen if I weren't on that tour.
Have an act that travels light....in a bag with a small table. Forget birds or animals. Have a close-up repetoire so you can do hospital wards if the occasion permits. Make sure they know you can do this. I did a number of hospitals in Vietnam apart from my regular USO unit that had three girl singers. We were small and easy to transport so we had our own helicopter. We went out to a number of firebases and worked in the morning and afternoon. We were always back in Saigon before sunset as it was too dangerous to be out at night.
Forget about a fancy manipulation act. A talking, comedy-oriented act with audience participation is what they want and what will go over. If you have anything that smacks of "magic for magicians," leave it at home.
The audiences will not have changed much from my time. I found they were all over the map from really appreciative guys to drunken Marines, but almost all were great....the best you'll ever have. Most of your audience will be young men, many away from home for the first time. Bob Hope made a career out of doing USO shows from WW II onward. His filmed TV specials were usually his USO shows, which did very well for Bob and the GIs.
Be able to do 10 - 40 minutes, depending on circumstances. Be prepared to walk out and do extra time if necessary. Don't be a prima dona. Don't make unreasonable demands on your unit manager or the local hosts. Learn to roll with the punches and expect the unexpected. Almost always your hosts will do everything they can to make your stay and your show as good as possible.
If you're not traveling with a big star, most of your performing venues will be varying degrees of primitive. Do your show, have a good time and it will be rewarding in ways you won't get from a high paying corporate gig.
One other thing - this may be the same as when I was working - you'll be rated both on the kind of show you do and on your off stage demeanor. You may have a fine act, but if you're a jerk off stage, you won't be back. Some acts were sent home before the end of the tour because of their off stage antics. The tour and the show aren't about the performers....they're about the service men and women.
Stay away from the booze because it is easy to walk into an officer's club or an enlisted men's club and have half the people there buying you drinks.
I came in off one USO tour and was asked to take another out right away because the USO found I could be trusted with both the entertainment and the managment. When they hand you $10-20,000 in traveler's checks to pay your unit over the tour, you know they trust you.