From the author's README on Thunderstore

Official GTA VI Merch

Available in Reskate now!

Excited for GTA VI? Me too, that's why I created this collection.

This collection includes 10 T-shirts, 6 Baseball caps.

19th November can't come soon enough.

Credits

All credits to the graphic designers @Rockstar

Real merch available from R* Store:

GTA VI Collection

Creator

ArnoldLeopold

Install GTA VI Official Merch Collection

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for GTA VI Official Merch Collection and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.