Time. Pick a date, a couple days if you can manage it, and take him someplace you'd both enjoy. You don't say where you are located (please change that!) but there are a number of farm-oriented museums and such in Iowa (Clarinda, Avoca, Sigourney come to mind instantly); I know there are similar in other states as well. You giving of your time will probably mean more to him than anything you could ever buy.