I reached a point where I couldn't get any further without figuring out the best way to make gold. Hopefully you can benefit from the evening I spent spreadsheeting.

This table lists foods and resting by their cost per strength gained. As of version 1.0.1, buying firewood from the Merchant in the Marketplace and resting at camp (Crossroads or Plain) is the most cost efficient, but takes more time since you have to go through the night/day animation each time. Buying eggs from the baker's wife in the marketplace (available after helping the baker at the inn) and making omelets in either camp is the most cost effective way of gaining strength by eating.

Many thanks to Thamior Silberdrache for pointing out that I had left out resting entirely.

Associated achievement: Have 100 or more strength


*Note: 10 water costs 4 strength which deducts 0.2 strength from each soup Judith makes. One set of ingredients makes two soups.

Many thanks to Matinny for pointing out that buying honey from the Beekeeper at the River and selling it to the Baker at the Inn gives 1 coin profit, but is a real time saver with fewer steps. There is a button on the left side of the trading window that allows you to change between 1x, 5x, and 10x quantities.

Selling grain isn't available until later in the game. The higher cost with the same profit makes it less efficient than honey.

There are several options for making a profit by buying materials, crafting them, and selling the result. "Make antidote from herbs" offered by the Alchemist at the River will net 4 coins per potion. Honey flowers are available from Gregory at the Crossroads and stingers are sold by the Alchemist. Antidotes can then be sold to the Apprentice at the Mage Guild.

Associated achievement: Have 900 or more gold in your inventory

Here's a list of merchants, their locations, and what they buy or sell. All item quantities are 1 unless otherwise noted and prices are in (parentheses) after each item. People or goods can be locked behind quests or enemies.