What are the most cost-effective healing / energy items?

The best bang for my buck that I've seen is the ice cream that's sold in the summer. As a bonus, it works as a gift for everybody I've met except for fisherman Willy and the girl with the blue hair who works in the saloon.

I'll also use things I'm gathering as I go along. When I'm fishing and I get seaweed or algae, no big deal. I'll eat it. Even a Joja Cola can give me a little bit of energy to do a couple more casts. In spring, the salmonberries are good freebies.

The cave mushroom is a must for 3 reasons: 1. Life Elixir (Hard to come by but can still craft a few) 2. Purple Mushroom (Lots of life mostly in the skull/mine levels) In the mine mushrooms appear on levels 81-119, but never ending on a 5 or 0. Level 83 often has mushrooms, once you reach the 3rd integer in the range, I would move on to next i.e., 83 reach and harvested, now go to 90. The reason is barrel platform levels often end in 4 and barrels don't give out mushrooms, and rare are both barrel platform and mushroom level combined if ever. 3. Fried Mushroom

Salad costs 220 and heals 50 Parsnip, Spring onion, Leeks, Eggplant, Cave carrots, grapes, crystal fruit, winter root, snow yam are all better to eat then to sell, esp parsnips. Hazelnut and Wild plums are much better in recipes.

Sashimi, but from carp, sunfish and primarily from 16 crab pots; doable.
Heals 33.

Berries esp. Berries (see below) with Double Harvest foraging perk @ level 4 foraging (chop down 64 trees before spring 15) i.e., after gifting I still had 257 salmonberries which will easily take me down to mine 120, by which time I will have sprinklers, gold axe and gold pickaxe. In the fall blackberry cobbler is must for mine in the desert.

Chowder; Put those clams to good use if not for speed grow then for chowder.
Heals 100, just add milk.

Lobster Bisque; yet another reason to have crab pots
Heals 100, just add milk.

Crab Cakes; Actually not that hard, you need sunflower seeds for oil, then wheat for wheat flour, crab and egg, but shouldn't be your go to.
Heals 100.

Eggplant Parmesan Heals 78 & +3 Defense for 5min (if used early enough)

Rhubarb Pie; very economical, just add wheat and sugar, and rhubard from Oasis for Year 2 Spring.
Heals 96

Glazed Yams: very economical, just add sugar!
Heals 90

Plum Pudding: Put those wild plums to good use, just add wheat flour and sugar
Heals 78

Roasted Hazelnuts: Use those darn things, 3 per cook, not other ingredients
Heals 78

Secret, Blackberry Cobbler: Make the most out of those black berries, just add wheat flour and sugar
Heals 78

Secret, Chocolate Cake: Make the most out of eggs, just add wheat flour and sugar
Heals 67

Secret, Poppyseed Muffin: Not just good for gift, but for eating Whoa!!! just add wheat flour and sugar
Heals 67

Secret, Cranberry Sauce: Make the most out of cranberries, just add sugar
Heals 56

Secret, What do you do with all the white & green algae you fished in the mine, you make pale broth and algae soup of course. Heals 56

I like the energy bars - it's easy to get the necessary acorns\maple seeds\pinecones just from cutting down trees. I'm early-ish game mind you, so this may not be the best answer.

Also, if you have the mushroom cave, you get many of those, and they can keep me going fairly well through a full cave expedition.

I like to use the fruit that I pick from the bushes as one source. Then when I got eggs I made scrambled eggs and omelets. Be sure to watch cooking show on tv to learn recipes and buy recipes from Gus in the saloon.