In 2017, the Washington Nationals had arguably the best back-up first baseman in the league in Adam Lind. Lind has a mutual option for 2018, and the Nats would undoubtedly want him back, but he may opt to test free agency.
As of right now, Lind is stuck behind Ryan Zimmerman at first base, so he would be limited to a back-up role with the Nats. However, with the way he performed in 2017, he would most likely receive some offers to be a starting first baseman or designated hitter in 2018.