Currently, I live in an area with no access to weights. I do a daily 15 minute ab workout, then 200 pushups and some light resistance weight training with whatever I can find around the house. If the weather's nice, I'll bike somewhere from 50 to 100 km.
When I'm in season, I'll swim a couple miles a day, plus some upper body weight lifting. This is the first summer where I haven't gotten fat, but I'm still losing muscle mass.