Most off season training off the gym premises could be performed with just your body weight or minimal equipment.
Make use of out-door gym, benches, stairs, bring some rubber training bands, it is easy to pack in your suit case.
We need to run through 6 muscle groups, chest(1), back(2), shoulders(3), legs(4), arms(5) and abs(6).
For keeping the neuromuscular connections many times it is enough to do just 1-2 full body workouts per week.
Do 3 sets of 15 repetitions.
Below are some samples of some easy training you can do at your house, when you are out walking/running or at some park or out-door gym.
When you are out walking or at home, benches and chairs can be used for various type of training.
Here are a few examples of leg work-out
Step-Up(4) Jump-Up (4) Bulgarian Split Squat(4)
Same bench/chair for triceps, chest and abs
Triceps Extensions(5) Chest Press(1) Seated Crunches(6)
For more legs and abs,
Walking Lunges(4) Plank(6)
Various types of rubber band can be used for
Biceps Curl(5) Triceps Extension(5)
For shoulders, you could use either a water bottle or bands to do front raise or lateral raise
Front Raise(3) Lateral Raise(3)
Also Dead Hang is a good shoulder exercise. Find something to hang, outdoor gym or a tree branch
Finally, to hit you back, here are a few examples
Single Arm Row(2,5) Bent Over Rows(2,5) Lat Pull Down(2,5)