Most anniversary programs have one gift and a changing number. It saves a decision and quietly undermines the thing it is meant to do, because the person at ten years receives what the person at one year received.
Tier it properly
One year. Acknowledgment rather than reward. Something small, good and useful — a quality drinkware piece, a decent notebook. The message is that it was noticed.
Three years. A step up in quality rather than category. Apparel works well here because it is worn and seen.
Five years. The first genuinely substantial one. A premium jacket, a good bag, a piece of tech worth owning — something that would not be bought casually.
Ten and beyond. Choice matters more than object at this point. A credit against a curated range respects that you do not know what a decade-long employee wants.
Presentation carries more than price
These are handed over in front of people. The box, the card and who does the handing over are doing as much as the item. A good gift presented badly reads as an obligation discharged.
Name the thing being recognized
A card that says something specific about the person or the work does what the object cannot, and costs nothing. “Congratulations on five years” is a category. The rest of the sentence is the gift.
Run it from stock
Anniversaries arrive continuously. A program that reorders per milestone runs out and finishes the year issuing something different, so the December recipient visibly gets less than the February one. Produce the year's quantity and hold it.
Do not let it lapse silently
A missed anniversary is worse than no program, because the absence is noticed. Whatever the tiers, the operational requirement is that the gift arrives on the date it is owed.
Employee programs covers recognition, and fulfillment covers shipping to individuals on a date.