I had some experience with that many years ago.

1. Get a mailbox at a UPS store or even a mom and pop post box place. The mom and pop ones will often do a bit more for you. Mine would forward specific pieces of mail to me or even open them and fax them if I so requested.

2. Membership at a gym/health club with plenty of locations in the places you'll expect to be. YMCA's are usually everywhere and LA fitness is very common out west. Keeping fit and clean does wonders for your self-esteem when everything else is going down the tubes.

3. If you sleep in your car outside of a regular camp area, expect some harassment from LEO and security.

4. Public Libraries are your friend. Lots to do, climate controlled, internet access, and long hours. Even if you are working/looking for work full time, there are still many hours in a day that you need to fill.