Move all your houseplants, if you have any, out of harm's way. Even if your cat has never shown an interest in any of them, if your cat isn't used to being alone, your plants may fall victim to his anxieties.
Step 2:
Leave out something you've worn recently, preferably on your bed or someplace else where your cat sleeps. This lets it have your smell and provides comfort for it while you travel. Be prepared to sacrifice it in the name of pet care, so don't go with your good suit or dress.
Step 3:
Set up extra water dishes. Like people, cats need lots of water.
Step 4:
Set out enough food for your cat. If your cat is a picky eater, a big bowl or extra bowls will suffice while you travel. On the other hand, if your cat eats everything set before him all at once, you might want to invest in a self-feeder from your local pet store.
Step 5:
Bring something home for it, whether it's an extra cat toy or some fresh catnip or other treat. Like human members of the family, your cat will miss you. Even if they proceed to ignore you for the next week, they still care. Turn your absence into something that ends well.
Tips & Warnings
Change the litter box before you travel.
Like the houseplants, anything that might be fragile and easily knocked off shelves or shredded by claws should be attended to prior to leaving.
These tips are only good for a few days' travel at most - such as a long weekend. Any longer than that, and you either need to have someone come by and take care of your cat, or put him or her up in a boarding facility until you return.