There are a number of ways to handle mail while on a trip. Frankly, mail handling is much easier for a full-timer than for someone with a sticks and bricks house who is gone on extended trips.
1. If you're going to be gone for 30 days or less, just have the USPS hold your mail for pickup when you get home.
2. If you're going to be in one place during your trip, you can either have the USPS forward your mail piece-meal or sign up for their premium forwarding service. Neither of these options work, however, if you're going to be moving from place to place during your trip, despite the previous poster's claim to the contrary. If you live in a small town and/or know your postmaster personally, they may be willing to work with you, but I wouldn't count on that, particularly if you live in a large metropolitan area.
3. Have a trusted friend/neighbor/relative pick up your mail, sort through it, and send you what you want/need when you call for it, just have several prepaid priority mail envelopes ready.
4. Sign up for a mail forwarding service and have the USPS forward your mail to that address. The only problem with having the USPS forward mail, whether directly to you or to some other address such as a mail forwarding service, is that some things cannot be forwarded, such as new credit cards and magazines will be forwarded for just 2 months. Before leaving on your trip, check to make sure none of your credit cards will expire during your trip. If one of them will, contact the Credit Card Company and have them change your expiration date so that you receive the new cards prior to your departure.