Comment by FooBarWidget

Micro exercises: It's nothing fancy. While walking in the park, watching the kids play, waiting in a queue or in the train or something, when you have a minute to spare, you can do wall push ups, isometrics, leg raises, step jacks, squats, row pull with your jacket against a pole, etc. Exercises that don't require equipment. If you get an exercise band then you can carry it with you (very light and compact) and then there will be more types of exercises you can do. This will raise some looks, but they tend not to be negative, some people even praise me for staying active in unusual contexts.

Another thing I can recommend is Chinese style radio calisthenics (guang bo ti cao, look it up on Youtube, all Chinese people learn it in primary school and do them daily at school). Full body cardio like and stretching exercises that you can do while staying in one place (you just need space around you). Takes 5-10m, better warming up than just walking and swinging arms and covers a lot of basic things. The entire approach seems virtually unknown in the west.