You can receive packages through your mail forwarding service, although this results in paying two shipping fees.
Leros has built a locker map to help find lockers and counters.
Google searches may also be used to find Amazon lockers. See sticky-bit's post google maps is a better interface for the nomad reddit post.
Many chain retail stores offer "free ship to store" (transfer, actually) to a branch near you. It may be also be called order pickup, in-store pickup, free pickup, etc. Payment is done on the website and the customer shows ID (Drivers License, credit card used in the order) to pick up the bundle when they arrive.
If the local Post Office agrees (ask the postmaster first), you may be able to send your package there as General Delivery. USPS offers GD as a service to transients.11).
Once received, the package will not be held longer than 30 days12), and 14 days is a common limit.
The mailing address will be something like:
Joe Walkabout General Delivery Sometown, ID 12345-9999
with the -9999 suffix indicating General Delivery.13) Be sure to ask if the postmaster has any special address or other instructions.
Local services like UPS stores may accept packages for a fee.15)