git checkout accepts an --ours or --theirs option for cases like this. So if you have a merge conflict, and you know you just want the file from the branch you are merging in, you can do:

$ git checkout --theirs -- path/to/conflicted-file.txt

to use that version of the file. Likewise, if you know you want your version (not the one being merged in) you can use

$ git checkout --ours -- path/to/conflicted-file.txt