Finding a gift dad will love can be a little tricky. The "perfect gift" can be elusive, but gifts that really nail the essence of the gifter/giftee relationship are the gifts that go over well and are the most memorable.
Luckily, to address this context, all a gift giver has do is remain C.A.L.M.
It is the thought that counts, so think about the C.A.L.M. approach and find dad a great gift.
C."C" is for conversation or chat. What have you and dad talked about recently? Lots of gift hints my have unknowingly been dropped. Did he just open the grill for the season? How about some grilling tools or BBQ sauces. A great gifter is often a really good listener.
A."A" is for affordability. This is pretty straight forward. Dad does not want you to break the bank on a gift for him. Both you and dad should feel comfortable with how much you spend on his gift.
L."L" is for likes. Think about a gift that goes with the things he likes to do. At the same time, think about if you feel comfortable getting him a gift that relates to his interests. Sometimes it's wise to steer clear of gifts that complement his life-long hobbies as gifts might be appreciated but also might not exactly hit the note.
M."M" is for modify. Modifying can turn a good gift into a great one. Think about the little (and often free) ways you can take a gift and make it better. For exmple, add a personalized note with "June 15th 2014" written on the inside cover of book you got him. It's just a little personal touch, but it makes the gift just a little more special.