not a gym bag per say but use it for my BJJ training. I always carry SISU thin mouthguard , tatami estilo 4 GI , water and that would be it
also i train for IPSC and in that beg I have my cleaning kit for guns ( balistol brushes and etc.) my guns currently have glock 19 gen5 sig sauer p226 tactical and springfield armory XDM