Step 1: Find the nearest bunker with a well-stocked fridge. Don't worry about the lack of windows, you'll be fine.
Step 2: Store canned goods like they're going out of style. Canned tuna, canned beans, and canned sardines. The more cans, the merrier.
Step 3: Learn basic first aid and practice your "I'm okay, I'm okay, I'm just slightly irradiated" face.
Need more tips? Atomic Tips 2: How to Build a Radioactive Water Filter