Carbon

When I drink alcohol, I get wood.

two Os

Grain!

both burn

does? reallllly? don't think they asked it quite like that either.

Both have the same origin: glucose. Alcohol is made by glucose fermentation and wood is made of celulose/lignine, that are basically a glucose polymerer.

They are both lighter than water.

both are integral parts in making a decent whiskey.

probably a minimum of a 100 things...which one do you want?

I have both in the morning.

Carbon

Both can leave you with a sore head, if misused.

Both are a fuel source.

I had the same answer as JJ. They are both less dense than water.

Neither one can climb trees.