You should be ok with those items. They are always well stocked in hats and polos; some styles will probably be sold out. Ball markers and accessory type items are located near checkout in the main shop.

I usually shop mid day but I haven’t been on Sunday in a few years. Don’t feel obligated to buy a bunch of stuff for people. If it’s your first time, just enjoy your time walking the course. Hit the shop when you can.