I can't believe I reached my mid-30s before this occurred to me. I'll loaf around, pre- and post-gym, in workout gear that never has enough (rarely any) pockets. In cold weather, a jacket or hoodie solves the problem nicely. But in the summer? You can wear a sleeveless hoodie.
There's a sort of effortless chic to this garment, and it will be forever in style. That's what I choose to believe, anyway. The secret to constructing it is (you'll never guess) to grab an old hoodie and cut the sleeves off. Bonus points if the sleeve cuffs are starting to fray but you just can't bear to part with it.
Be conservative at first, try it on, and trim more if needed. When you're happy with one side, fold the hoodie in half so you can cut the other side to match. Then parade around with your phone in one pocket, your keys and wallet in the other, ready to respond to all compliments with "Thanks, it has pockets".