After having used one for work for over a year now, I would definitely buy the Milwaukee jobsite backpack (Model 48-22-8200) as a dedicated track day bag.
https://www.protoolreviews.com/tools...-review/12941/
The back pocket has a laptop sleeve and is deep enough to accomodate shoes and some riding clothes. A helmet can fit into the front bulk pouch. There are plenty of pockets inside that will hold your tools, and there is enough room in the tool section to accomodate a chainring bag.
Just weighed my work bag and it's been holding 52lbs of tools daily for the last year and a bit, so it is durable and will last.
Edit: The CLC (Custom Leathercraft) 1134 backpack is a less expensive yet similar version. It seems to be larger, just not as durably built.