I can tell you personally that this is a tough one. I actually chose the same topic (retail/grocery checkout) for my Sr. project and there is so much that can be done, that if you actually start looking into it, you’ll see there’s been a ton of ideas already piloted. Now in the real world this is one of the key areas I work in, and even then it’s still just as challenging. Not only do you need to bring a cool design, but you need to show a business that investing in a fancier cart will bring them value.
The # of challenges are there, and the problem I found was actually figuring out which area to focus on. Justin pointed out you can look at the whole experience, but to me that becomes dangerous…there are dozens of retail experiences out there, ranging from typical grocery, personal shoppers (where you scan your items directly), self checkout, or even digital storefronts that you’ll see popping up now where you just scan some barcodes printed on a poster and your goods come out a shoot. All are unique and good in their own ways, but it makes a tough ID challenge for a student to solve…because big businesses have been trying for years and still haven’t done a great job.
My advice may be to think about it the opposite way - go into a very specific niche, focus on something you can do real research for, and kill it with awesome execution. IE what if you picked a very specific store or user group (mom with kids, seniors, etc) and tried to do something that really served that user group or the brand itself.
It’s not looking at the big holistic experience, but I think it gives you material to do a great project. You can do some parts of it that show how you’ve considered the big system, but if you’re looking to do product when you graduate (vs experience, or branding or strategy work) then that’s how you should tailor the project. There’s a lot of nice details that could go into the cart…where to put your purse, cell phone, how to deal with germs - even consider talking to some stores about how they buy and service/repair the carts. Maybe there are opportunities to save money in shipping or on repair labor. I think if you could capture those insights and put them into a sweet project, you’d have something pretty good.