This invitation idea is a lot of fun - both to give and receive through the mail.
What you need
Plastic soda bottle
Shredded paper filler
Theme related trinkets
An example of a theme would be to a Halloween party. You could use a bat shaped invitation, black paper filling, plastic spiders, tiny pumpkins or candy corn.
These can be hand delivered or sent in the post.
Cut an X in the side of the soda bottle.
Through this X, put invitation, filler and various small items into the bottle.
Tape X shut, cover with label that has been addressed with a marker.
Looking for another fun way to give an invitation? Check out these Party invitations that are made using a puzzle template, the invitee has to put the invitation together like a puzzle. Check out these party invitations you can buy on Amazon