If you regularly entertain, you'll need a few bigger pieces. Even to cook for yourself, though, you need the right tools.
1 full set of measuring spoons and cups
Cutting boards (for meat, produce, bread)
Heavy-duty knives (chef's knife, paring knife, bread knife)
Nonstick and stainless-steel skillets (small, medium and large)
Small (4-cup) heavy pot with cover
4-quart pot (for pasta, soup, blanching)
Nonstick omelet pan
2-3 wooden spoons
Metal slotted spoon
Storage containers with lids
Organize a pantry for one. It will give you a base on which to build many meals.
Olive and vegetable oils
Toasted sesame oil
Vinegars (red wine, balsamic, cider)
Grains (couscous, bulgur, quinoa)
Prepared chicken and beef broth
Jarred pasta sauce
Canned tomato sauce
Peppercorns (if you have a grinder)
Dry herbs and spices
Canned fish (sardines, tuna, salmon, anchovies)
Unsweetened cocoa powder
Assorted dried fruits
Most contents of the refrigerator will frequently be updated. There are some staples that should be maintained.
Cheeses (cheddar, mozzarella, Parmesan)
The freezer is the single diner's best friend. Bulk foods can be divided into smaller portions and frozen. Vegetables can be blanched, then frozen. Nuts freeze well, as does butter. Just be sure everything is labeled and dated. When you add new things, move the older items forward.
Ginger root (makes it easy to grate)
Cooked/raw meat in small portions
Frozen vegetables (peas, spinach, edamame, corn)
Frozen fruits (berries, pineapple, mango)