Parking Trick
Have you ever noticed that when you park your loaded touring bike the front wheel tends to move and turn on it's own account causing the bike to fall over? This little trick holds the wheel straight when the bike is on the kickstand.
I use an octopus strap that is made of elastic and has a hook on either end. One end attaches to the rear water cage, and then the strap runs through the front wheel. The strap on the other end attaches to the other side of the rear water cage.
There are several other methods available. Depending on your brake lever setup, you may be able to jam a small screwdriver or rod through the lever mechanism to hold it on. Other people use a large rubber band to pull the lever and hold it so the brakes remain on.
I have found that by locking the brakes, the front wheel is sometimes still prone to swinging in either direction and possibly making the bike and trailer fall over. I prefer this method of running a strap around and through the wheel.
If you have a BOB trailer or similiar type of trailer, some people recommend jack knifing the bike and trailer. This will hold the bike upright but it tends to exert pressure on the trailer swing arms and the chain stays of the bike. If the bike is heavily loaded as well I don't recommend this method of parking. I tried it once and one of the fingers on the trailer's mount is slightly bent.
The trailer was not designed to be parked this way with the bike. I have also found that the front wheel is still prone to swinging around. I have gone to the extreme once of unhooking the trailer when I needed to park as there was nowhere to lean the bike. I now carry the strap with me, and I keep it well rolled up when not in use. If the end of one of these octopus straps gets caught in your gears it can do all sorts of damage.