It is best to have a friend or family member back home, to serve as a 'permanent address' for mail and financial matters, possibly even giving them a Power of Attorney for handling urgent situations that you didn't anticipate, and cannot be handled by express mail. They can use email to a large extent to keep you informed, and to send the value of bills so you can pay in a timely manner.
If they aren't close enough to check your mail, you can have it forwarded to them. If you need it mailed directly to you, a mail-forwarding service can collect mail from your home, or a post office box, and send it to the last address you give them. You can phone-in a change and they will mail to the new address immediately. About US$140 a year for all services (postage to re-mail, trips to PO, etc.). You can let creditors know that there may be about a 45-day delay so they can adjust the due date.
Leave small care-packages with a trusted individual back home, who can send them in times of need. You may be able to give their phone number and address to others who need to contact you. It is a good idea to leave a copy of your address book and online-files with a 'home manager', so they can email, fax, or mail it if you lose your copy.
"Leave a record of all important information with them, including but not limited to, known itinerary (as far as is possible); lists of Poste Restantes that you will check with approximate dates; copies of important documents, e.g. passport, visas, insurance papers, numbers of travellers cheques, bank accounts, credit cards and so on. (Watch out for expiry dates on credit cards -- will you get caught out?)" <Chris Finlayson>
"We wrote a letter every six to eight weeks to all our friends and relatives. We sent the letter to our designated mailer, who we equipped with mailing labels before we left. All our friends were thrilled to get these continuous dispatches about our trip." <Larry Lustig>
"Be sure your care-packages have some blank checks, including ones for any line of credit you may have (including the one on your credit card, if checks are available)." <Larry Cotter>