I've used general delivery through the US Postal Service on occasions when I wanted to ship something but didn't have a new address yet.
It's really quite easy. Address your parcels to yourself, General Delivery, in the place you're going. The post office will hold the mail for up to 30 days. Present your identification at the post office to which you sent your mail, and you have your packages.
Make sure you include a return address on your mail. If for some reason, you don't pick up your mail, the post office will need to know to where it can be returned.