The other invitees are catcher Jordan Procyshen, outfielder Brian Bogusevic and right-handers Kyle Kendrick, Chandler Shepherd and Ben Taylor.
After the trade of Yoan Moncada to the White Sox for Chris Sale, Devers will be the Minor League position player Red Sox fans focus on the most in the coming year.
Travis was a standout performer last Spring Training for the Red Sox, but he suffered a season-ending torn ACL in his left knee while playing for Triple-A Pawtucket in May.
Castillo, who hasn't lived up to expectations after signing a seven-year, $72.2 million contract as a Cuban free agent in August 2014, was taken off the 40-man roster last June. Perhaps the 29-year-old outfielder can demonstrate some improvement during camp.
The Red Sox don't have a lot of outfield depth in the upper Minors and may need Castillo if one of their regular outfielders is injured. Castillo will earn $10.5 million this season, and the Red Sox owe him a balance of $46 million through 2020.
Craig, once one of the most reliable run producers in the National League, has been in a free fall since his trade to Boston on July 31, 2014.
In fact, the outfielder/first baseman spent the entirety of an injury-plagued 2016 season in the Minor Leagues, appearing in just 29 games. Craig, a World Series hero for the Cardinals in 2011, is owed $20 million over the next two seasons. His contract includes a $1 million buyout for a club option of $13 million in 2019.
Devers was named Red Sox 2016 Minor League Defensive Player of the Year after committing 15 errors over 117 games (116 starts) at third base with Class A Advanced Salem, leading Carolina Leaguers in fielding percentage (.960), total chances (377), putouts (104) and assists (258) at the position.
Before the injury, the 23-year-old Travis played in 47 games at Triple-A Pawtucket and hit .303.
Castillo broke camp with the Red Sox last year, but was sent to Triple-A when manager John Farrell couldn't find enough playing time for him. His power has declined since coming over from Cuba. Castillo hit just two homers in 395 at-bats for Pawtucket in 2016, adding 20 doubles, five triples, 34 RBIs and nine stolen bases. He did finish strong, slashing .328/.369/.445 over the final 49 games.
In the 32-year-old Kendrick, the Red Sox have added a veteran with 212 career starts and 41 relief appearances at the Major League level. Kendrick is 81-81 with a 4.63 ERA for the Phillies and Rockies.
Bogusevic, 32, returns to the United States after spending last year in Japan, playing for the Orix Buffaloes of Japan's Pacific League. The left-handed hitter most recently played in the Major Leagues for the Phillies, hitting .259 in 22 games in 2015.
Procyshen has been with the Red Sox organization since being selected in the 14th round of the 2014 Draft. He spent all of 2016 at Salem.
Shepherd, a reliever, had seven saves and a 2.81 ERA last year over 40 appearances split between Double-A Portland and Triple-A.
The 24-year-old Taylor is another homegrown product, taken in the seventh round of the 2015 Draft. He notched 98 strikeouts over 79 innings last year for Salem and Portland.