For buying on the fly prepackaged, high or higher cals/oz ratios than more commonly found, easily repackaged/amended on the fly, versatile, flavorful, not boring, AND with short ingredients lists or with ingredients I can understand without having a degree in nutrition here are some options.
Trader Joe's Roasted Coconut Chips - 160 cals /oz, about $2 for a 2 oz package
Try adding a little tang occasionally by mixing with orange or pomegranate infused dried cranberries. Or, try Bare, Danielle, or Dang brands that come in a Carmel and Sea Salt version. Can be mixed into a trail mix with just about anything.
http://www.traderjoes.com
http://www.baresnacks.com/products#c...-coconut-chips - several other dried foods including dried apples
http://daniellechips.com - lots of other rather unique chips
http://dangfoods.com/shop.php
Trader Joes Flattened Banana -about 125 cals/oz, about $1 for a 4.4 oz package. YES, these meet the above criteria, consider the price, volume, delicious taste, convenience, alternative to carrying a fresh banana, and the ingredient list - JUST BANANAS. Great for an on the fly snack or adding to other foods like a grain/oatmeal b-fast. Make sure you have your toothbrush ready after eating.
I Heart Keenwah Snacks - 130 cals/oz, about $2-3 for 4 oz package, these are snacks largely made from Quinoa. Try with a nut butter, dried fruit, or cheese.
http://www.iheartkeenwah.com/snacks/
EARTH BALANCE Coconut and Peanut Butter Spread - about 170 cals/oz, about $1-1.80 for 1.15 oz squeeze packet, luv this stuff for it's prepackaged convenience when I don't make my own version ahead of time and place into a squeeze tube, non-GMO/Gluten Free/Trans fat Free/Vegan, Combining these two ingredients into one - a trans fat Free/low sugar PB with coconut products is one of my favorite high cal/oz, low volume, tasty UL food tips/treats.
http://earthbalancenatural.com/produ...-squeeze-pack/
WILD SQUIRREL/WILD FRIENDS(found under both names) Vanilla Espresso Almond Butter - about 170 cals/oz, about $1.50/1.15 oz squeeze packet. This is what you get when two savvy intrepid Foodie college students get the funding(on SharkTank) to introduce to the public a darn tasty backpacker friendly product. Absolutely delish! - almond butter, caffeine, dash of salt and vanilla all in one squeezable convenient packet. I luv this stuff. Check out there other varieties too.
https://www.wildfriendsfoods.com/single-serve