Trumbo, who had a standout spring at the plate, batting .297 with six home runs and 20 RBIs in 25 games, will see time at first base until Kendrys Morales comes off the disabled list.
Conger, another standout, hit .231 in the spring, with nine hits and six RBIs in 18 games.
"We have a little bit of wiggle room and can keep some catching depth for a while," Angels manager Mike Scioscia said. "How we sort that out past it, we will wait until we are there."
Vernon Wells (left field), Peter Bourjos (center) and Torii Hunter (right) will start in the outfield with Bobby Abreu, who will serve as the primary designated hitter, and Chris Pettit in backup roles.
Pettit, who hit .260 this spring with eight RBIs in 24 games, is seen by Scioscia as a player who can give the team a lot of different looks.
"He is one of the outfielders that was really on our depth chart," Scioscia said. "He provides coverage in left field and can even play a little first base. He puts in a good at-bat and can pinch-run."
The starting rotation consists of Jered Weaver, Dan Haren, Ervin Santana, Joel Pineiro and Scott Kazmir. Pineiro (right shoulder tightness) will start the season on the disabled list but likely will return to start the home opener on April 8.
In the bullpen, the Angels will have only one left-hander to begin the season, Hisanori Takahashi. The other relievers include closer Fernando Rodney, Jason Bulger, Kevin Jepsen, Michael Kohn, Rich Thompson and Jordan Walden.
Starting on the DL will be Piniero, right-handed reliever Bobby Cassevah (right shoulder inflammation), left-handed reliever Scott Downs (left big toe fracture), Morales (left ankle), infielder Freddy Sandoval (left oblique strain) and outfielder Reggie Willits (left calf strain).
Right-handed relievers Trevor Bell, Matt Palmer and Francisco Rodriguez were optioned to Triple-A Salt Lake, along with infielder Andrew Romine.