I want to add a gift wrap with some products in Magento 1. How can I do this?
You can do this with a Custom Option on the products you want Gift Wrap adding.
Catalog > Manage Products > Select Product > Custom Options (Tab at the bottom of the list)
Magento 1 Guide to add Custom Options: http://docs.magento.com/m1/ce/user_guide/catalog/product-options-custom.html