As far as pay goes, if you're part time, don't expect anything above minimum wage. You have potential to get a raise around 6 months to a year, but by then minimum wage will have risen to your new salary and you won't be getting a raise again to offset that.
Also, with the pro of keeping yourself busy, the con comes when there aren't enough employees around to do anything more than make sandwiches, which means you fall behind on all your other tasks that need to be done. Subway will only hire just enough employees to keep up with customer flow, and in my small town Subway, there was a time where only 5 people worked there. It can make it difficult to call in sick or ask for days off when there is nobody to take your shift.