If sending one of the employees a couple of bucks via PayPal or something similar, to ship it for you is not an option, this is what I would do:
Order a free flat rate box, and ship it to the restaurant: Click Here
Pay for a label on USPS's website and email it to the restaurant. Alternatively, you can print it out and mail it to them. Click Here
Perhaps something like this?
USPS will ship an empty prepaid flat-rate box. The large size box is almost $60. I believe you fill out the label when you purchase the box.
Some USPS boxes have tape already applied but I seem to remember that the similar large priority flat-rate box doesn't. You may want to ask the restaurant if they have package tape. If ...
The key is to minimize the amount of "kitbuilding" the restaurant needs to do, because it may be asking a lot for them to receive a box, print out a label, coordinate a pickup, etc.
The DIY (slow) option
USPS has a variety of Priority Mail boxes which ship at a flat rate (weight does not matter). You walk into the Post Office, look at the boxes, decide ...