Coupe of other thoughts on merchandise:
1. The merchandise building is a little overwhelming. You're going to be shopping with what feels like 5000 other people jammed in there with unlimited options on shirts, caps, sweatshirts and literally everything else you can think of. Have a list of people with sizes you need to buy for. You'll end up buying more, but make sure you have your must buy list with you.
2. They have shirts hanging on hangers in the middle of each room and you'll be tempted to grab those for ease. Don't. Decide what shirt you want and then go to the counters where you'll get the same shirt but which is folded in a beautiful clear plastic Masters bag. Much easier to pack and much nicer to give to friends/family than one on a hanger.
3. They have mini merch stands around most of the concession areas on the course with limited selection of caps, flags, t-shirts and stuff like that. If you forget somebody or, like me, decide "you know, I need another three caps and a couple of flags for the hell of it", they're very handy so you don't have to wait in line for the main merch building after you've been in there.
4. The line for the merchandise building is always long. It's like a Disneyland line for a popular ride on a holiday weekend. I wouldn't look at the line and say "we'll come back." Get it over with.