Of course you wouldn't start a garden full of tomatoes or zucchini or any other heat loving or long season plants. However, you could plant a small patch of salad or other leafy greens, turnips (hurry though- my dad has a rhyme about planting turnips, and while I don't remember how it goes exactly, it says to plant them in July), or fall peas. The heat will help the seeds to germinate quickly, and they'll be up just in time for the cooling weather that they thrive in.
Or you could use this fall to prepare a garden for next spring. Spring is, in a lot of ways, the worst time to start a new garden. Who isn't super busy in spring? There is so much to do, and all you really WANT to do is go outside and have fun- hike, bike, whatever your outdoor activity of choice is. Besides, if you start a garden in spring the work is backbreaking. Start it now and you can let other elements do the work for you.
How much you do this fall depends on two things- how much time and money you have now, and now easy you want it to be next spring. The easiest and cheapest thing to do is lay down something- cardboard, a scrap of carpet, some sheet plastic- to kill the grass (weigh it down as needed). However, this will result in a little more work in the spring, as you'll still have to move your... whatever and turn the soil a little. With a little more work and money, you can create a garden that is ready to plant at your leisure next spring- lay down cardboard or any other biodegradable material (newspaper, paper feed bags, paper grocery sacks, etc). On top of that layer at least 5 inches of compost or soil, covered by another thick layer of wood or straw mulch. The mulch will keep weeds at bay, encourage microbial and worm action in the soil (eventually breaking down the paper, after it's done the job of smothering the grass underneath), and preserve moisture. Next spring you simply need to neaten things up and stick in your desired plants (move mulch to the side for anything you direct seed, then replace mulch as the plants mature).
My point- now is not a bad time to start planning and do some of the work for a garden. And a garden can save you a lot of money in a short period of time. Starting and maintaining a garden can be as cheap or as expensive as you want it to be- mulch can be found for free in many communities (grass clippings, community mulch piles, or wasted hay from farmers) and cardboard can easily be obtained from friends or from stores- most have a surplus they would gladly give away. $10 of seeds and about $5 in tomato plants can provide you with most of your vegetables over the course of the summer, with extra to "put up."
Just like I think everyone should own two or three chickens, I also think everyone should have a garden. Unless you live in a studio apartment with no windows. In which case I would say you have other problems...
If you have some space, though, think outside the garden. In most climates fall is a good time to plant fruit trees and other edible perennials. While most involve a few years of waiting, fruit trees are an easy and relatively low maintenance way to grow food.
Some more links on starting new gardens or gardening in small spaces:
My Simple Country Living's Farmgirl Friday, Real Food Forager's Fat Tuesday,