You should be manually resolving all merge conflicts before re-staging them ("git add") and completing the merge commit.
The only way to "accept both" would be to just re-stage (marking as resolved) the conflicted files without resolving them ( >>> and <<< would be there still), but your result couldnt be compiled or executed. And this is terrible practice, even if you make commits later to resolve. The point of the merge commit is to see the resolution of the merge in the commit.
There are ways to avoid generating the conflicts - using merge strategies. For example, you can pass a strategy parameter to the "git merge" command to always take your change in a conflict using the "ours" strategy. Look at the "git merge" help page to see the different strategies and maybe one will apply to your situation.