So, not a very flashy product, but a necessary one for me: my staple lip balm. I'm not a lip gloss girl but I love lip balm. I feel like if I don't have any with me, I'm going to be distracted by my dry lips literally all day. And lip gloss just doesn't cut it. I've tried a lot, but ChapStick's Moisturizer lip balm is my absolute favorite.
This particular one moisturizes my lips the best. It's not sticky or waxy, and it actually sinks into my lips so they feel conditioned later. It's available everywhere (shown here in an awesome 3-pack) so it's easy to find. Believe me, this stuff works in all seasons, even in the driest of winter weather. Plus, it has SPF 15 (which is great, because I don't think a lot of people realize how easily sun damage can happen to your lips). Guys can use it, too--it doesn't leave your lips shiny and doesn't have a crazy smell. 
Final verdictCost: $1-$2 for a single one, about $3-$4 for a value pack. Cheap enough to buy as many as you need--one for the nightstand, one for your purse, that one you left in your pocket, the one at your desk . . .
Moisturizes: This is the only one I've found that actually leaves my lips very moisturized, without any waxy feeling.
Repeat offender: I can't tell you how many of these I have. Like I said, I get really weird if I don't have any ChapStick, so I've bought a million of them to keep everywhere. It's my most basic staple beauty product, and I can't live without it!
-T
