7/11 is a good place to start working. You start at minimum wage, however the experience you get will be so much more compared to others. You will experience better customer service interaction since you mostly deal with people. During summer times you get more customers, which allows you to adopt to a high stress environment. You also work with 2~3 people which allows you to increase your experience with working in a team. Sometimes you have to work by yourself during certain hours. They also let you handle forcasting and ordering food and products. This gives you valuable experience in predicting the weekly and monthly goals of the store, as you have to take into consideration the month, promotions, events, and weather when you order them.
7/11's strength is also it's weakness. While it is good to start here, it is not that great to stick for a long time. First of all because of it's minimum wage start. Secondly, the overall atmosphere and goals of a store depends on the manager. I have worked with good managers and I also have worked with bad ones and I could definitely see the impact it had towards the store. Lastly, it depends on the location you are at, but some locations are just riddled with people which you can safely say are the "Trash" of the society. Dealing with them may increase your skills in handling customers but the stress adds up.