Places giblets into wrap pack, then wrap pack into cavity.

a piece of card placed in a cover of philatelic origin in an attempt to enable the cover to go through the mailstream without damage and/or to improve the quality of any postal markings placed on the face of the cover.

an advertising circular that is enclosed with other material and (usually) sent by mail

A promotion piece mailed with an unrelated communication. The latter could be an acknowledgement form, shipping notification or invoice.

a craftsman who stuffs and mounts the skins of animals for display

One who, or that which, stuffs.