What if anything is appropriate as a gratuity for an invitation to hunt on private property.
A friend of a friend kind of deal.
I dont want to insult the land owner either way.

Since your post is under bird hunting, I would consider the circumstances. If it is a "social" dove hunt with a couple of dozen or more people there, a polite "thank you for inviting me" and " I enjoyed it." would be enough in my opinion. Being helpful if the occasion arises is a BIG plus. Just offering to shuffle people around or whatever will get your "name" on his list. If it is more personal, say 3 or 4 guys pheasant or quail hunting, then I would consider something on the order of a nice bottle of wine, whiskey, (obviously if he drinks said items)or a couple of boxes of shells to be a nice, but not necessary gesture. If it is really top shelf, then you might consider a good hat (gift certificate), a Filson product, or something along those lines. The first thing I would do is ask the friend what he thinks and go from there. You can rarely go wrong with a good bottle of bourbon or scotch, which is almost always appreciated and won't break the bank (some bottles of Scotch excepted). Even if they don't drink it, you can bet they know someone who will.

I agree with Gatogordo, completely .. A bottle of Scotch is always a good idea .. Even if the chap doesn't drink (it), often a person entertains guests who might prefer it .. Touch of class in my humble opinion .. Just don't buy 8 year old stuff ...

Sour mash works better for me. I use it to make cough medicine.