What use are Chocolate Bars

candy - health regen, will increase every time you heal. Better not to use it often.
chocolate bar - weapon enchantments
lollipops - convert two lollipops to one candy

also you will get "pain au chocolate" later, with it you can boost your stats (HP/DMG/Cooldowns)

According to the Candy Box 2 wiki, you can only get 13 chocolate bars total:

• You can buy 1 at the shop.
• You get 1 for throwing 1630 candies on the ground
• You get 3 for answering the squirrel's questions
• You find 1 in the cave
• You find 3 beneath the tree, after finding the map (rocks) in the cave
• You find 4 in the hole

Without resorting to any sort of cheat/glitch, if you've used your 13 chocolate bars then you're out of luck.

However, there is currently a glitch involving the text-save/load feature that allows you to earn more:

• Go to Save, click Get Current Game as Text and copy the text
• Start the game over (refresh the page), and get enough candies to get the Save feature again
• Paste the text into the bottom text box and click Load
• You can now re-earn the chocolate associated with the cave. That means you'll find one more chocolate in the cave and, once you find the cave-rocks again, three more beneath the tree.

You can repeat this to gain as many chocolates as you want.

You could also edit your save file.

Follow the steps above to copy your game-state as text, then find the section with the text number gameChocolateBarsCurrent=0. Change the 0 to whatever value you want, then load the game.

Finally, once you beat the game, you can use the computer to give yourself more chocolate.