After having hunted freelance style for a long time...
Any gesture for a landowner is much appreciated. The following is my formula for a welcome back...
My wife hand makes a card for them. The ticket here is to hand write a note specifically to the landowner about your hunt, their property and hospitality and how much you appreciate them. I also print a picture from our hunt showing how much we enjoyed ourselves. The card is sent within a week of our trip.
Close to a holiday we will send a smoked ham or turkey. We have also shipped knives, pocked multi tools, gift certificates, shelled pecans, etc. The cost does not matter. It is truly the thought that counts. Just show them that you care and treat them as you want to be treated. Don't get so hung up on the amount of your purchase.
Lastly, stop buy and talk to them personally. Take an interest in a relationship with them. Oh, don't wear out your welcome, either. Get enough spots rounded up so the farmer does not see you on his place every weekend. A good hunting friend to them is one that comes around once or twice a year, rekindles a relationship, treats the land with respect and shows their appreciation.
This formula takes work. However, if you follow these simple steps, or your modifications thereof, you will be welcome back for years to come.