Mailing address while out of the country?

It's called a Private Mail Box (PMB)

They are run by private companies. The number one player in the field is The UPS Store,* however many smaller businesses also exist. Your address becomes

 Your Name
 Their Storefront address #123**   (your unit number)
 Their town, ZC 12345

These differ from a Post Office mailbox in several ways:

• They are more expensive, but allow month-by-month billing
• You can call them up and have them bundle up your mail and ship it to you UPS, DHL, FedEx, Priority or Express Mail, after sorting out what you want and holding or discarding everything else as you direct
• Outfits which insist on a street address (no PO boxes please) will accept them
• Unlike PO boxes, all shipping companies can ship to them.
• They can accept large (truck) packages, certified mail and other things that need signing for. I once got gym mats.
• Can usually give 24-hour access. The store is designed with the postboxes in the very front, and rolldown doors or gates to separate the mailbox area from the rest of the store. You are issued a key to the retail store's front door. No kidding.
• Some can open your mail and scan it
• They can help you package and mail almost anything via any carrier
• Some have limited copy and print ability, like a Kinkos (FedEx Office)

The upshot is that having a PMB makes your problem rather easy to solve.

And when you return, it's all just handled. No spending a day contacting 40 different vendors and government agencies about your new address, having a few rarely used ones slip through the cracks like IRS or DMV. Having moved every 6 months for a chunk of my life, I found the PMB absolutely indispensable. I carefully chose a location at a transit hub, for easy access. As a bonus I also don't have ten "past addresses" on my credit report.

* UPS bought out Mailboxes Etc. for this purpose and to quickly establish a nationwide retail presence, similar to how FedEx bought out Kinko's.

** The Postal Service has regulations on this, lightly enforced. #123 is allowed. PMB 123 is allowed. APT 123 is not allowed. STE 123 is not allowed. Essentially you're not allowed to fob it off as your domicile or office. I have never had a problem with anyone being willing to deliver mail there. A very few are savvy to this being a PMB and want a real street address also, but they happily send all my mail to the PMB.

A P.O. Box is the best option. You can set one up at your local post office, and set up online payment so you don't have to visit the post office to pay rental fees.

Also, I'd recommend you set up mail forwarding so that mail to your residential address goes to your P.O. Box instead of your house, and won't be returned undeliverable when your lease expires.