Lemonick has juvenile diabetes - the disease was diagnosed when she was 7 years old.
Her bag's stash is to counter a glucose crash, which can cause Lemonick to feel dizzy and make her hands shake. She said a crash feels similar to being out in the sun too long.
Lemonick has not suffered one during a game this season, but has felt "shaky" a few times during practice, she said.
Last week, as the Rams were preparing for a crucial league game, Lemonick asked her coach if she could take a break and go to her bag on the sideline. Her hands were starting to shake. The sugary snacks would quell that.
The senior defender monitors the disease constantly. She injects herself with insulin and checks her blood sugar four to five times daily, even during the school day.
She pays even closer attention for about 90 minutes before games and overly hydrates.
Despite the disease, Lemonick has excelled. Harriton coach George Dick said she is "super mature" and a "role model."
"It forced me to grow up a little bit quicker than the average first or second grader," Lemonick said. "I'm appreciative that I'm able to be so independent and mature quickly. It makes me a stronger person in the long run."
She is one of the team's captains and was a key piece of last season's state-championship squad. She ran cross-country in the fall and captains that team, too.
Lemonick will play lacrosse next season at Cornell, and she is the state's top senior player, according to Inside Lacrosse.
She started playing defense before her freshman season, at Dick's request. It was frustrating at first, she said. It is hard to fill a stat sheet on defense.
Lemonick grew into one of the area's top one-on-one defenders, and she plays against the nation's premier talent during the summer club season.
She plays her best against top competition, when her 5-foot-7 frame matches up against bigger opponents. She's strong (175-pound bench press) and fast (20-minute 5k).
No longer worried about stat sheets, Lemonick noticed that the other things she was doing - plucking ground balls, winning draws - were just as important.
"The little things can end up winning or losing a game depending on how close the game is," Lemonick said.
She learned last season to take draw controls, the girls' equivalent of a faceoff, and has shared duties this season with teammate Sabrina Tabasso.
The trick to winning draws is something Lemonick said most players do not do. Instead of listening for the referee's whistle, Lemonick watches the referee's hand before beginning the draw.
"I've heard from a couple people that sight is a little bit faster than sound," she said. "Right as her hand goes, I try to get the first step and the first jerk of my stick."
The district and state playoffs are creeping near, causing Lemonick to keep an even closer watch on her blood-sugar levels. The games are bigger now, she said. And she can't let diabetes stop her.
If Harriton is going to make a run at a second straight state crown, the Rams will need their star defender. And Lemonick will keep her backpack stuffed to ensure she's ready.