Not an exhaustive list, but here's some of what I usually have on hand (including fridge/freezer items that keep a long time):

• Pasta (various kinds but usually at least spaghetti and shells)
• Canned beans (I usually have black beans and chickpeas + sometimes others)
• Canned tomatoes
• Chicken stock (either in tetrapaks, cubes, paste or some other shelf-stable version) -- sometimes other kinds of stock (e.g. vegetable stock too) but usually at least chicken stock
• Salt, Pepper, MSG + a good selection of various dried herbs/spices/seasonings (e.g. basil, oregano, cumin, cayenne, garlic powder, etc.)
• Soy sauce
• Vinegar
• Olive oil
• Neutral vegetable oil
• Butter
• Canned fish (at least tuna and/or sardines)
• Cheeses (I usually have Parmesan, pepper jack, and American cheese slices that melt easily [e.g. velveeta or kraft singles or something like that] plus sometimes cheddar or Swiss)
• Peanut butter
• Flour
• Baking soda
• Yeast
• Chocolate
• Cocoa powder
• Sugar
• Eggs
• Milk (UHT lasts a long time)
• Salsa
• Canned or frozen green vegetables (e.g. peas, spinach, etc.)
• Rice
• Bread (frozen for storage)
• Dried lentils
• Dried fruit
• Cornstarch
• Ground meat (frozen)
• Tea
• Ketchup
• Mustard
• Mayonnaise

(may add more to this as I think of things)