I had a client postpone a session recently so she can get her Christmas shopping in without her baby. I half jokingly told her to do lunges down the isle of the store and not to take the escalator or elevator. Instead take the steps and skip every other one on the way up.
Like I said I was half joking but the half that wasn't really thinks that this is a good idea. You might get strange looks but it's a great way to get your training in while doing shopping. The people that are looking are probably the ones that need to do this the most. They will probably just go to their cardio theatre and watch a movie, but that's a topic for another day.
Don't even get a cart at the store. Use the items you pick up as weights. If your grocery shopping grab some gallons of milk and do presses, curls, rows, swings, rack squat....etc... The possibilities are endless.
Point being, if you are dedicated and serious about training, it can be done anytime, anywhere, any day!
Even though these kids take it a little far, here are some things you can do. Just don't do push ups like this. ELBOWS BACK!!!!!!!
Food Store Training
Rock n Roll
And if you do take a cart get one with a broken wheel. That is a good challenge.