Another vote for the BLT&A (avocado), especially in mid to late summer when fresh tomatoes are available at the farmers market (or in the garden).
Toasted sourdough bread, thick cut peppered bacon, a massively thick slice of a fat heirloom tomato, sliced avocado, and lettuce for whatever reason lettuce is needed. Mix it up a little to keep things fresh by adding some grilled jumbo shrimp or a grilled lobster tail sliced to fit, swap out the bacon for country ham (or just add the ham to the bacon), mix in some arugula or watercress with the lettuce for a bit more flavor...
Very flexible sammich.