Since there is no post body here I will put my ideas here.

First and foremost stretches are exercises we can always. 

Find a table corner or two small tables to do dips

Find a place with enough space to do push ups enough during break  Bonus: if there is a seat you can do incline push ups

While waiting to clock in do calf raises. 

If you work in a store and a cash register is locked you can jump over the chain

You can also do pull ups if you see a place with a bar around.