At age 16, it will be difficult for you to find anything else but don't rule out a grocery store just yet. In a grocery store, you don't have to apply to work in the front end if you don't want to. You could possible work in the grocery department. There are usually night shifts where you can block shelves. Blocking is where you take all items that are in the back and out of place on shelves and you stack them in the front and move them forward to make them look neat. The job could be boring but customer interaction would only be limited. Customers on occasion may ask you where an item is but other than that, there's much less customer and co-worker interaction.
I've worked both departments in my younger days and they are like night and day. The front end is being either a cashier or a service clerk and you have to see people constantly. As a cashier, you pretty much have no say in anything you do. I hated it because I hated being stuck in one spot for 4-5 hours all day. Service clerking isn't as bad as cashiering because you can go outside and collect carriages but there's still a lot of being told what to do. Also in the front end, you have to work with multiple co-workers during your shift and you're bound to have to deal with some that are obnoxious.
Working in grocery is much better for introverted people. There are positions where you can break down grocery pallets and put them on u-boats and fill up shelves with the ordered product but those jobs either are during the morning or late at night when the store is closed so a 16 year old wouldn't be able to get that position, but don't rule it out in two years. If you block shelves at night, you usually come in after the morning crew has already gotten all the product out on the floor so often, all you have to do is find an aisle that is really messy and fix it up at night. Often you get to work by yourself since there usually is only one person who blocks the shelves at night. The nighttime supervisor may ask you to do a few tasks like fill sales items, dairy products and bread but other than that, it's a self managed role.
I know I perhaps went on a bit of a tangent here but I worked for a grocery company for many years so I know everything there is to know about the grocery business.
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"The less I know about other people's affairs, the happier I am. I'm not interested in caring about people. I once worked with a guy for three years and never learned his name. The best friend I ever had. We still never talk sometimes."
