Coffee. Iced coffee costs more than hot coffee, and while your daily cup seems like a minor expense, those few cents add up. The decision on whether or not to go hot or iced is also one of the most immediately affected by the weather. So, if it's warm several days in a row, you'll drink more iced coffees, and you will pay more for it.
Driving. This is a no-brainer, but it's worth reminding ourselves: Gasoline usually gets more expensive in the summer because stations actually stock a different, pricier grade of fuel starting around Memorial Day. At least this is a built-in expense that kicks in on a prescribed date. A post on How Stuff Works explains the difference in depth, but basically what you need to know is this: "Summer-grade fuel is more expensive for two reasons -- because of the ingredients it contains and because refineries have to briefly shut down before they begin processing it. Summer-grade fuel also burns cleaner than winter-grade fuel."
Eating. Food prices are going up worldwide, and that's due to a lot more complicated factors than just the weather. But the warmth does come into play when it gently propels you out the door to your favorite restaurant, in particular one with a patio. "Typically in the restaurant industry, the summer is always your higher volume. You’ll also have your spikes in the holidays," said Paul Paz, a 35-year veteran waiter from Portland, founder of WaitersWorld, and co-author of The Professional Server. "Absolutely weather has an impact on whether people go out. Here in Oregon we’re so notorious for our wet weather, when the weather gets nice, it’s like I didn’t realize how many people lived in Portland."
Drinking. Summer is a time to vacation, and vacations are a time to drink, so a lot of us wind up with heftier bar tabs for that reason. But it's the hometown tippling that's going to kill you. In New York, for example, you can't get away from pricey rooftop bars and extended-stay happy hours on summer Fridays. If you live in a place like New York or San Francisco you live in a place lots of people want to take vacations, and when the weather's nice they'll want to take more of them, and they'll want to stay with you. That means lots more catching up with your old, freeloading friends at (where else?) a bar. "I’ve worked in multiple places and some of them have a noticeable spike in customers during the summer," said Maurina Lioce, a longtime New York bartender. "Also people come in earlier in the day." A note to guests: Buy your hosts many rounds of drinks. This will be expensive. Budget for it.
Flying: Airfares are expected to go up this summer, and to stay high throughout the travel season. That doesn't necessarily have to do with the warm weather -- rather it's thanks to higher oil prices. But the extended pleasant snap means there's a longer window of nice weather in which to vacation, so you'll probably be tempted to do so more than once. You'll have to pay handsomely for it.