LA Times health writer Jeannine Stein has some practical suggestions about how to turn everyday environments into very low cost (OK free) exercise equipment:
The beach: Sand is your friend. Wet or dry, it adds resistance when
you’re running or walking.ÂÂ
The park: Jungle gym equipment like rings, bars and low balance beams can be used for pull-ups, push-ups and crunches. Use them.
The trail: Instead of striding up a hill,
try walking lunges or traveling squats  or just hop or skip up the
incline.
The city: Take the stairs. Don’t even think about the elevator. In fact, take the stairs two at a time, go up and down sideways, or hop from
one step to the next for a plyometric workout.
The link above didn’t work for me. Here’s the link to the story:
http://www.latimes.com/news/custom/scimedemail/la-he-outdoors-gym-20100719,0,7097571.story