You can receive packages through your mail_forwarding, although this results in paying two shipping fees.

Amazon will ship to an Amazon locker.¹⁾

Walmart will ship (transfer, actually) to any WM near you, no shipping charge. It will be bundled up in the old Layaway area in the back.²⁾

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.³⁾.

Once received, the package will not be held longer than 30 days⁴⁾, 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.⁵⁾ Be sure to ask if the postmaster has any special address or other instructions.