Are you paying too much for travel expenses?

I assumed everyone knows about getting the lowest rates when traveling. On some recent trips I realized many are paying top dollar for things like hotel, rental cars and airfare.

I know there are many ways to save and I will not go into all of them, just the ones I am using now.
First of all I have found for booking most hotels and rental cars I use Hotwire.com.  I have been getting rental cars for as low as $9 a day.  I paid $15 a day for a car on the Big Island of Hawaii.
One of the ways you will pay top dollar for rental cars is walking up to a counter and getting what they have.  At this point you are most likely paying the top price.  You need to go online and book ahead of the time. When I do this with Hotwire.com some of the bookings require you to pay ahead of time.  This is where the biggest savings take place.  If your schedules can change at a moments notice on a regular basis, then this might not work for you.
I always fill up the rental car before returning it and this usually is a lot less than paying for the rental car to do this for you.  It is great just to bring the car back with whatever is in the tank, but for this convenience you will pay for the service they offer.
I try and book all my flights with the same carrier.  Since I live in Atlanta I have chosen to do this with Delta.  The advantage of frequent flyer points is more than just a free trip, the more points you get a chance to board early and be sure your luggage is stored in the overhead containers. 
Another advantage of building points is getting 2 free bags and 20 additional pounds per bag.  This is important for photographers who often must check things like lighting kits, which can weigh more than the normal 50 lbs.
After traveling for a while you start to know the going rates.  When prices seem a little higher, I then will depart from my normal Hotwire.com and try going directly to the hotels or other services.

By booking with Hotwire you still get to use your hotel chains reward points.  So I have joined Priority Rewards, Hilton Honors and Marriott Rewards.  Sometimes I must weigh the travel time between the hotel and the events or airport and the choice is not just based on the lowest price but how much time I will be spending to and from those locations.

I am sure there are tips you can give to me as well.  Take a moment and let us know some additional tips for the frequent traveler that will make their travel more enjoyable in the comments below.