I would get away from the idea of training "arms." That's reductionist thinking.
Instead, train movements: pushing and pulling. The arms work in tandem with other muscles to push or pull far more than they do things in isolation. You can do this with bodyweight, and the various stretch cords/tubing which pack up small and light.
Examples:
Anchor a stretch tube and do chest presses and rows.
Using bodyweight, do pushups or any variation (from the knees, yoga style down dog etc) You can also just lean forward against a wall and push back. Vary the resistance by how far away you stand from the wall. For pulling, get a towel, loop it around something sturdy, lean back and pull. Just like with wall much ups, vary the difficulty by where you put your feet. When camping, I often do these movements using a picnic table. I use the bench for push ups, and hang underneath grabbing the edge to pull.