Chances are that you're groomsmen aren't all going to be so close that they can be walking everywhere, especially to the wedding, which means another way of travel will be in order. Seeing as there are 250+ million cars in the US alone, the odds are leaning towards a trip by automobile. In fact they're sure to be driving around to a lot more places than just the wedding. The thing about driving is that with all that cruising fun comes a lot of responsibility, and paperwork. Good thing your groomsmen gift choices are wide and varied, because knowing how much they will be, and do, drive means you can choose to influence that driving in a good many ways. It would probably be a good idea to stay away from flasks for now, however nice, and stick to something a little more driver friendly. The gift should be personal and usable (not something that's going to get thrown in a drawer or closet) which should line up a few great choices, namely a CD holder or glove compartment organizer, though you could always be a little less pushy on the organization and give them gifts that are similarly organizational but with a few bits of hardware that any guy will wish he had when he needs to figure something out with his car. And with a little personalization your groomsmen will feel your thanks and be thankful themselves, just the way any friendship should be.