I'm another Jersey Mike's fan but, at the cost, I've been making my own.
One tip I picked up off of a YouTube video is to wrap your sub tightly after making it. I wrap it tightly in parchment paper and then wrap that in foil and stick it in the refrigerator. In fact, I just finished making one for lunch - ham*, salami, pepperoni, provolone, mayonnaise, hand shredded lettuce, and thinly sliced tomatoes. It's 10:30 Am, here and it will sit in the fridge until about 1:30. I don't add the olive oil, red wine vinegar, and Italian Seasonings until just before I eat it, so that stuff doesn't do bad things to the lettuce while it is sitting.
* I use Krakus Polish ham. It is available at the deli counter at my local Safeway (Albertson/Ralph's family). I'm of Polish heritage and it's taste brings back memories of my Mom buying a 5 pounder of Krakus in a not quite oval shaped metal can that came with a metal key for opening it - which I can't find anywhere. The deli counter slices it very thin for me and at $8.99/lb. it is cheaper and, to me, more delicious than any Boarshead ham.