Aerobic activity, strength training and flexibility (stretching) are very important for the body. If you are looking for alternative ways to get these exercises without the tradition gym equipment, there are lots of options, but I wouldn't be looking to avoid these exercises. For aerobic activity, think of anything that you like that will get your heart rate up and keep it up. Running, biking, swimming, dancing, skating, skiing are good options.
For strength training, all you need is your body weight, you don't need a gym full of fancy machines, or even dumbbells/barbells. Pushups, squats, and dips are some examples of exercises you can do anywhere without equipment. You can use household items (liquid jugs, soup cans) for added resistance. Personally, I like working out with my TRX suspension trainer, Rip Trainer, and Bodylastic resistance bands. These items are very lightweight and portable, and I can take them anywhere with me.