For a ton of sandwich ideas, I heartily recommend Max Halley's Max's Sandwich Book: The Ultimate Guide to Creating Perfection Between Two Slices of Bread (eG-friendly Amazon.com link)
Both the author and the book are very entertaining and it has pages of mayo variations (which can be made from scratch or by mixing in to mayo from your store-bought jar) but if you're not interested in investing in a sandwich book just to amp up your turkey sandwich, I'll share Max's secret to deliciousness - every sandwich should contain these 6 things:
- hot - The warm item may not be particularly handy if you're packing a sandwich and eating on the run but if you're using nice roast turkey, packing it separately and warming it gently in a microwave or toaster oven with a bit of broth definitely amps up a sandwich. Max is not a fan of cheese on sandwiches unless it's going to get warm and melty so sliding the cheese-topped bread into the toaster oven or broiler is another way to get a warm note.
- cold - Mayo is almost always going to be cool or cold, same with pickles.
- sweet - A relish can be both sweet and sour. Ditto pickled onions. Adding mustard and or hot sauce to jam makes a good sandwich condiment.
- sour - This can be as simple as a squeeze of lime or sprinkle of vinegar and might well be incorporated in one of the other ingredients like pickled veg. One of Max's mayo mix-ins is malt vinegar and it certainly amps up the mayo. I've made the piccalilli from the book and it's great on sandwiches as is sauerkraut or kimchi
- crunchy - Some options for crunch are bacon crumbles, pork rinds (scratchings, chicharrones, scrunchions or whatever you call them) potato stix, French fried onion rings that come in a can, any kind of flavored potato chips, kale chips or deep fried ramen noodles or sweet potato starch noodles.
- soft - Often this will be your meat or a spread. Guacamole, hummus, peanut butter, egg, avocado, even butter are all soft elements
As far as bread goes, Max is a big fan of focaccia for sandwiches and I agree. I like to make my own, freeze it in sandwich sized slabs and heat it up in the toaster oven to get some nice crispness. Depending on the fillings, he also recommends baguette, mini-ciabatta rolls, English muffins, brioche.
Edited to add that if I made that all sound too complicated, just try to get contrasting flavors and textures into your sandwiches. The temp contrasts are nice, if possible.
