Like others have said, make sure the lettuce is next to the bread. This way the tomato juices won't soak into the bread. If you are making a wrap you can also cut the tomatoes in half and then use a small spoon to remove the pockets of seeds, which also contains the juicy stuff.
You can make it different by using Virginia ham - it's a bit sweeter tasting than normal deli-style ham. Also, peppered ham is wonderful!
"Count yourself...you ain't so many" - quote from Buck's Daddy