Doughnuts and coffee are complements; tea and coffee are substitutes. Complementary goods are goods used in conjunction with one another. Tennis rackets and tennis balls, eggs and bacon, and stationery and postage stamps are complementary goods. Substitute goods are goods used instead of one another.

The easy answer if to go traditional; these six (or seven) teas will work with any cafe or restaurant and be perfectly acceptable to any tea drinker you encounter: English Breakfast, Earl Grey, Peppermint, Chamomile, Green Sencha, Lemongrass & Ginger and optionally Masala Chai.