I doubt you could become a steward for the summer, stewards require a large amount of training on a frequent basis so training you so that you only work 8weeks isn't really worth while.
It's not really a part time job, its more a full time career.
My brothers doing Mechanical Engineering at University and loves it, it's a hard course but there are several areas within the engineering industry that you can get a career in (for example motor sports).
I wouldn't touch the other degree.