With Joe Hart justifiably left out after a poor season for West Ham United, Southgate has Stoke City's Jack Butland and Everton's Jordan Pickford vying to start in goal with Burnley's uncapped Nick Pope putting pressure on both.
Long-time goalkeeper Joe Hart and injury-prone midfielder Jack Wilshere were omitted, for example.
The Reds will spend four days in Spain ahead of the Champions League final, though Alexander-Arnold got a surprise on the day of their flight when he was included in Gareth Southgate's squad.
Central midfield seems light on experience and cover - Jordan Henderson and Eric Dier are the only real mainstays - but Southgate is confident the likes of Loftus-Cheek and Jesse Lingard can fill in.
"The first call-up for Trent Alexander-Arnold is well deserved", Southgate said.
"It's an honour to be named in the England squad for the World Cup".
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The players flying to Russian Federation were unveiled in a video lasting one minute and 44 seconds with youngsters announcing each squad member's name.
Defensively England have plenty of options, although centre backs Gary Cahill and John Stones lack authority which is why Southgate is likely to favour a three-man defence featuring Kyle Walker with two attacking wing backs.
"The selection process has been over months really, it's not just been the last few weeks".
He was included in a provisional 35-man squad which was submitted to Federation Internationale de Football Association at the weekend, prompting Eddie Howe to leave him out of the Cherries team at Burnley on Sunday.
"We feel the team are improving and we want to continue that momentum".
He joins Tom Heaton, James Tarkowski, Lewis Cook and Adam Lallana in being placed on the back-up list.
England will play two matches before travelling to Russian Federation on June 2 against Nigeria at Wembley and on June 7 against Costa Rica at Elland Road.