I’m being dragged back into my Zombie apocalypse Heathers au special interest, so it’s time for headcanons!
Chandler would wield an axe, specifically one of those red fire axes
Veronica would be extremely skilled with a hunting knife
Duke would be able to learn and actually enjoy using a bow and arrow, but she also knows how inefficient it can be, so she’d also have a hatchet or machete 
McNamara wouldn’t have the heart or guts to kill, even when absolutely necessary, and so rather than waste everyone’s time and even resources trying to teach her to use something she’d be the team’s medic.
Duke is the smallest and most capable, besides maybe Chandler, in battle so whenever the group finds a small space that someone needs to go into they’ll always send Duke. They know if something or someone is on the other side the girl can defend herself
Veronica, due to how many friends she’s gained over the years, is most likely to recognize a stranger the group comes across
Chandler’s family has a log cabin in the middle of nowhere in Maine that the group decides is their safest option to stay
Chandler becomes the go to killer when something or someone needs to die. Chandler will kill with no hesitation if she thinks she has to no matter how much it might hurt.
McNamara gets more clingy during the apocalypse and never leaves Duke’s side. She starts to get separated anxiety if she’s away from anyone, especially Duke.
Duke helps McNamara study medicine and anatomy. Even going out of her way to secretly look for and grab any books she thinks might help.
Veronica is the most hopeful in the group. Hoping, but doubting, that the government will come save them or they’ll find a safe community.
Chandler never expressed wanting either of her parents when everything was normal, but after the apocalypse starts and the girls start to get more and more traumatized and stressed Chandler starts wanting her mom more. Even occasionally crying and silently praying for her mom to come help or save her while the others sleep.
Duke is really good at cooking, but doesn’t like to cook much.
Chandler knows how to start a fire and cooks whatever food they end up finding whenever Duke doesn’t want to cook (which is 90% of the time)
Chandler has some basic survival skills from going on hunting/camping trips with her dad.
Whenever the girls loot a store McNamara will leave money on the counter just so she doesn’t feel like she’s stealing. For peace of mind. (This one is from @willz0)
The girls start to cuddle with each other originally to stay warm during the cold nights, but eventually they can’t go to sleep without their cuddle buddies
Chandler and Veronica always cuddle, and Duke and McNamara always cuddle
At some point Veronica finds a CD in a store the girls are sleeping at and a CD player that surprisingly works. The CD is of Capital Cities “In a Tidal Wave of Mystery”, but the only song on it that Veronica recognizes is Safe and Sound. Regardless she puts the CD in and starts dancing and singing to it, purposefully dancing in a way at Chandler to try to entice her to join her to have some fun and relax for the first time in weeks or months. Chandler eventually gives in and the two temporarily forget their stresses and worries as they goof off. Duke and McNamara watch fondly and may or may not join them by dancing together too.
Courtney would be one of the first people to die and chandler would take her tennis racket and use it as one of her weapons (credit to @phoenix-duke for this headcanon. You Courtney X Chandler lover, I see you.)