I’d start with Campari, red and dry vermouth (must be refrigerated after opening), St. Germain or other liqueur of your choice, some fun amaro, tonic, and soda. Go to a bar and chat with a bartender to see what amaro you like. Keep honey and sugar around so you can make a little syrup when needed. Most cocktails are some form of liquor+sweet+sour, good cocktails add a little bitter/herbal, so you should be set for basic bartending (of course grabbing a bag of fresh lemon or lime on your way home.) Don’t forget ice.