If I'm understanding this correctly, you receive a parcel with various assorted items in it. You choose something you like, and replace it with something else of an estimated similar value, and ship it to the next person on the list?
If that's the gist, is it too late to be added to the list? Sounds fun!
There are a few keys rules:
1. You must NOT apologise for taking ages to send the parcel back out.
2. Make sure the parcel weighs less than 2kg. This keeps the postage at £2.95.
3. Take all you want out of the parcel - no limit! Just make sure there is still a variety of choice for the next person.
4. Don't steal the parcel.