Sometimes my 'gift' is the item priced so low I don't really make a worthwhile profit...  (In other words, some of my items are loss-leaders and I couldn't afford to sweeten the deal with something else...or maybe I just don't want to. Some others are handmade and the prices are often lower than most other people would charge for similar work). 

I generally include a little something extra for repeat buyers, or buyers who have purchased multiple items in one transaction, but not for standard, single item transactions.