What kind of alcohol should we use for this DIY-Whisky kit I got my partner for our anniversary?

Not entirely sure what subreddit would be best for this question so feel free to point me in the right direction if I am misplaced. So I bought a do-it-yourself whiskey set for my boyfriend for our anniversary. It came with like different dried flavorings and woods that you put into a decanter along with “a neutral grain alcohol”. What should I get to use?