It’s halfway through May and you still haven’t booked a summer vacation? Relax. You actually may be in luck. Because so many people have booked their vacations already, travel sites are looking to fill holes in their inventory -- and that means deals for you.

“Mid-May brings a big push for summer vacation packages and hotel deals,” said Brent Shelton of shopping deals site FatWallet.com. “Hotels and tour operators look at where they might have some low inventory and offer deals to get you to book. It’s really good for the consumer who hasn’t decided where to go yet.”

Of course, you have to know where to look. Start by checking out deal sites like Groupon, Amazon Local and LivingSocial. Groupon has a section devoted to last-minute travel deals, but you’ll find savings in its general travel section as well. Recent deals included deep discounts at Greer Lodge Resort & Cabins in Greer, Arizona, and a Texas wine country getaway for half the normal price.

(Once you know your destination, be sure to also look for deals on activities in those destinations. Sites like Groupon and LivingSocial often offer deep discounts on tickets to museums, festivals, tours and other attractions. They want to fill their inventory too, explains Shelton.)

Plenty of travel booking sites are offering promo codes for additional savings on top of promoted deals. LastMinuteTravel.com, for example, is giving an additional $40 off with the code MOM40 until May 31. To find such discounts, look for them on travel package sites’ social media accounts like Twitter and Facebook. You’ll also get access to flash sales that may only be promoted to social media followers.

You also may get an additional discount by downloading and booking through a travel site’s mobile app. A recent TNS Global vacation survey found that 14 percent of Americans will book their travel through a mobile app -- and the industry wants to boost that number. So sites will offer incentives, like LastMinuteTravel.com’s $25 off a hotel booking through its app.

Finally, it’s worth it to create an account at a cashback site like FatWallet.com, which adds an extra layer of discounts to the deals companies are offering. Here’s how it works: You click on the links through FatWallet’s portal on your way to book your trip at a travel site, and FatWallet will give you a certain percentage of cash back on the booking. You only need to create an account with FatWallet using a valid email address.

FatWallet’s new Hotel Deals portal offers up to 10 percent cash back at 100 popular online travel sites such as Priceline, Expedia and Hotels.com. And because it’s prime booking season, says Shelton, many of the merchants FatWallet works with have increased their cashback bonuses to stay competitive.