If working in a shop that is understaffed, and there are lots of customers, and you are at the till, struggling to keep up, what should you do if there is no help available?

In a professional manner, make an announcement to your customers that you are on your own at the moment and want to help everyone as best you can and that you would appreciate their patience and you will do the best that you can to help everyone as quickly as possible.
I think it's the only thing that you can do.

Be polite no matter what; speed is important but don't sacrifice efficiency, so pace yourself. Try to focus on your current customer - appologize for their wait, ring them up, bag 'em, thank 'em, and do it again with the next customer. Every two customers check to see if more help is coming.

tell the customers to be patient enough as there is going to be some delay and that you are gonna do as fast as you can. later talk to your admin. about it.

Do the best you can. And let people practice the art of something that is in very short supply in this society. Patience.

Not much you can do, but keep ringing people up until the rush is over.

Where I work, we coach our employees to take two orders, bag up the first one, take a third order, bag up the second one, take a 4th order, bag up the 3rd one...basically take orders until you have 2 people waiting to get their order and then get one of them. The exact # of orders you want to take before turning around to get them would depend on how long it takes to assemble the order. If you have to assemble each order, it would make sense to just take one at a time.

The main thing would be to smile, be polite and apologize for the wait. Most people don't mind waiting a little while for great service and quality.

never let the customers know you are by yourself (some will take advantage). Say a staff member is taking a bit longer upstairs than anticipated but won't be long and that although there is just you, you will endeavour to be as efficient as possible and ask that they be patient. That's usually done the trick for me in the past.

I work in a shop and if i get a long queue i smile and just say i will get to you as soon as i can,and i leave it at that people are usually ok about the wait.