It depends...
No pun intended. But realistically, are you going to be able to shower and clean up daily? If so, then just wear a diaper as needed. "Depending" upon the incontinence need, use a full sized diaper if you are likely to experience uncontrolled and continuous wetting, but if it is slight and only a chance of slight wetting, then use something such as Depends Real Fit. The latter is highly discreet and likely not to be noticed.
There is more risk of embarrassment of leaking than in admitting you need to wear protection. If this is your first summer working there, then talk to the employer about your need and don't stress over it. I can almost with certainty guarantee that if you need to wear because of medical need, no employer is going to look less upon you for sharing that you need an accommodation for this. How do I know this? Well, first of all, it is against the law to do so!!! And if they hired you because of your skills for doing this job, they are going to want to help you be successful and not have incidents that could cause you to be less than successful because of embarrassment or otherwise.
Be truthful about your condition. If it is minimal and something you can take care of without much notice or adaptation, then certainly do so. Otherwise talk this over with your employer. If they are any company or agency worth working for, they are going to be there to help you and not think anything less of you for it. If they aren't, then it is a good thing you talked with them and found this out as they aren't worth working for. Tell them to kiss off and find a real company to work for.
Just don't stress over it. There is absolutely no reason to do so.
:detective3
Teddy Bear Cowboy