As far as upper body exercises go, can't do much better than pushups and pullups. You could try variations of each. Here are some cool ones that I had my LTs do when they were trying to get into Ranger School:
Pushups: Feet elevated, Plyo Pushups, Clapping, Handstand pushups, and my personal favorite Ring Pushups
Pullups: Mixed Grip, Rope Pulls, Towel Pullups, and Ring Pullups
The final SUPREME upper body exercise is the muscle up! Either on a bar or rings, it is an awesome total upper body exercise. Tough as crap to do!
Some workouts I like to do for Pushups are:
1. 50, 40, 30, 20, 10 with 30 s rest between sets
2. 20 pushups, every minute on the minute for 10 minutes
3. Tabata Pushups - 20 s on / 10 s off for 8 sets, for max reps
Some workouts I like to do for Pullups are:
1. Countdowns - 10, 9, ... , 2, 1
2. 3 x 5 of 5 sec let downs
3. Death by pullups - add 1 pullups every minute until you can't complete the amount in the minute. Break up the reps however you want. For example, Min 1= do 1 pullup, Min 2= do 2 pullups, .... Min 10= do 10 pullups
Core work is pretty random, cause concentrating on your core during pullups, pushups, squats, etc, will do most of the work for you. After that, planks, side planks, glute bridge, Hanging leg raises, knees to elbows, toes to bar, flutter kicks, six inches, (could go on for days but it all does the same thing).
Also, putting on wieght begins and ends in the kitchen. Unless you eat more, you won't gain weight. That simple. Good luck.
