With every holiday like this it's very personal to your family/what your child-dad relationship is like as to what present you buy, but I think a mug is always a good bet - find something cheeky and something that applies to your relationship. Cufflinks are always good (of course only if your dad wears cufflinks) and personalising them like the ones above always make a good present. The sweet jar above is a good idea, but I think anyone could create something like this themselves - just find a supermarket or a sweet shop and go crazy! Or if you know of a particular sweet he likes, just buy a mug, buy some sweets and there you have it - a perfect present! Also this makes the mug easier to wrap if you have something in it!
Happy spending (but don't get distracted.... maybe I should listen to my own advice sometimes...)
Love, peace and chocolate,
Curly Cutie xxx