I can see if you've never had a lobster roll, or even lobster itself, before you might want to try it as unadulterated as you can, but after that first time you really don't feel the need to repeat the experience. Especially on the same vacation.
I need my lobster to pop damn it!
Step 1: Ingredients
For the sauce, or dressing if you prefer, you'll want to make about one and a half or twice as much as you think you'll need. We'll get to why in a bit. How much you make will depend on how much lobster you have and how saucy you like it. You should be able to tell if you'll need a half cup, cup, or more by looking at the size of your pile of lobster and estimating.
I like a combination of sour cream and mayo. The sour cream cuts the fat a bit and mellows down the mayo. Primarily you'll have mayo, maybe two parts mayo and one part sour cream. Start there and make it more or less as you taste it and figure out what you like. Salt and pepper it to taste.
I've always liked a little tarragon with lobster. I would have used fresh, but it was vacation and the rental already had some dried on hand, so bam! And we'd also brought an old container of Faux Bay Seasoning (generic Old Bay Seasoning) and threw in a touch of that.
Onion and garlic. I used very little garlic, fearing that it would be to strong. You can forgo that if you wish. But all lobster rolls need a little onion, and sadly I've never had one at a restaurant that did. Make a fine dice of onion and add as much as you like to your sauce.
Now take half of your sauce and toss your lobster with it and set it in the fridge to chill out for a few hours. Do this at breakfast to have for lunch or at lunch to have for dinner. Why half? Because the lobster will weep out some liquid and turn it all into a loose sauce at the bottom of your bowl.
When it comes time to assemble your roll you'll want to strain off that runny sauce and taste your lobster. FOR GODSAKE TASTE IT! You may think it's fine as is, or you may want to add some of that reserved sauce. Figure it out and then let's roll.