I know when I was an SETL I'd had stock bags as a closing routine. I also know if I came in every day as a cashier and had no bags- I'd grab some from another register, ask a leader for assistance and talk to my leader about my concerns.
As for the only cashier thing, Target has for a while think that from open to 10 am is ok for minimum staff to work. All you can do is try to speed up the check out process and express concerns with your leader