I had In & Out once in Vegas - it was great. What does that sauce taste like again? I can't remember - but I remember liking it.
I had Carls Jr in Vegas. It was pretty good. Here in Texas I like Braum's, but I don't think there are any in the Houston area.
Before I die, I WILL eat at an In-n-Out - even if it means to pay $500 bucks for an airline ticket, find one, eat there, and then immediately fly back home.
Make it animal style. They give you grilled onions, double the lettuce and tomatos for free. You could animal style the fries too. They put an extra layer of cheese with grilled onions, but it costs a little more.
I guess that works if you want a vegetable sandwich. (a little off topic, but does anyone else feel that too many veggies detract from the quality of a burger? by, you know, hiding the meat?)
You could order it protein style. They take away the bun and wrap the burger in a lettuce leaf. There's also 4 by 4s where they stack up four buns, four patties in cheese. There's no meat hiding there.
Believe it or not, my brother, who doesn't eat red meat, introduced me to the "Veggie Whopper" back in college. It is, essentially, a whopper without the meat. I'll be damned if it wasn't tasty. I hardly even noticed the meat missing. (though I suspect that might have been due to the buns going through the grill.)