What can you do if you cannot go to the gym to workout?

Run on actual pavement and body weight exercises. Hell, I'll start doing a set of pushups and it's not long before my daughters are climbing on my back during my set. Who needs a weighted vest when you have children.

I'll make it simple, listen to those NCOs that posted below me, lots of good advice.

No one needs to go to the gym tow workout. People have been getting in and staying in shape without gyms for hundreds of years. One can run/job/walk almost anywhere you wish; at any time you wish regardless of weather.
Weights? There are rocks everywhere, of varying weights and shapes. Get creative. No need for some overpriced DVD that's hyped up to get you in "Warrior" or "Insane" shape in a month.

Get your workout done at home, outside. Go run, do HIIT, Calisthenics w/ pylometrics. Just because you can't get to a gym doesn't mean you can't workout. Get one of those DVDs for Insanity, P90X; find a good tree limb and do pullups.

YouTube is full of various trainers who do body weight only exercise programs. Mastering your own body weight is way harder then throwing some weight on a bar.

One of my former bosses always carried a Kettle bell for PT. He had lots of TDYs and it became a way to stay in shape in the hotel. Not all hotels have gyms.

Walk, Hike, fish, climb, horseback riding ANYTHING just Get out of the house and into nature!!

The world is your gym.
We had no gym for first 6 month of Iraq so we made routines with isometrics (body weight exercise pre cross fit era) made weights and pull up bars and did army PT. You figure it out if your commited.

Eat right because you can't out train poor nutrition.

we have a free gym just outside your front door !!