The Aston Villa defender went head-to-head with some of the biggest names in the sport while playing for Poland.
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He faced Lionel Messi's Argentina in the group stages and got his hands on the seven-time Ballon d'Or winner's shirt, with a little help from Villa teammate Emi Martinez.
The 25-year-old then went up against superstar forward Mbappe as Poland were knocked out of the tournament in the last 16.
Cash also managed to get his hands on his jersey after the game and he is taking no chances to make sure they don't mysteriously go missing.
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"I've got hand luggage here," Cash told talkSPORT. "From Qatar to Dubai I made sure those shirts were right with me. I put them in the safe in the hotel room as well.
"It will be going on the hand luggage with me!"
The Villa man will now have a short break in Dubai before heading back to England ahead of the Premier League resuming on Boxing Day.
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Their first match back is a tough test against Liverpool and Cash believes he heading back a more experienced player.
Cash continued: "Playing against those sorts of players is really good and those sorts of teams as well. Played against Argentina, France and Mexico, they are fantastic sides.
"For me, personally, I have gained so much experience and it has been a different learning curve in the last couple of weeks.
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"I'm sure when I get back to Villa it will benefit me massively.
"Now I've played against those top players, I'm looking forward to playing against even more top players week-in, week-out in the Premier League.
"Liverpool are right up there."
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When asked if it has been a better experience at the World Cup than he imagined, he added: "It was more [than he expected]. What I've learnt and gained is more than what I thought it was. I came up against the likes of Messi and Mbappe, for a young growing player like me it was massive.
"I've learnt so much over the last couple of weeks and gained loads of different things. It is more than I thought."