It's a cleaning pen—Tide To Go. You drink a little Gatorade, and it drips on your shirt.... I'm really picky about stuff like that. It would drive me crazy if I had a red spot on my shirt all day.
For ball markers I always use a quarter that was minted in the '60s, like in 1962 or 1963 or '67 or '68. In high school I started doing that, and I've kept doing it ever since. Why the '60s? Well, you want to shoot in the 60s. Sometimes people suggest I use one from the '50s, but I don't want to get greedy.
SWISS ARMY KNIFE
Just in case. You never know when you need to use a knife to cut something. Like a coupon.