ひとつにまとめてもらえますか？って英語でなんて言うの？

You can say it in the following ways: -Please put everything in one bag. -Please put them all in one bag. -Can I get one bag for everything? -Put them all in the same bag, please.

You can say "put it all in one bag." or if they ask you if you want different bags you can say "just put it all in the same bag." You can also use the colloquial term "bag it up together" which means put it all in the same bag. In the UK we have to pay for plastic bags in supermarkets and so it is good to take your own bags to the supermarket to avoid this charge.

examples "Can you pack them all together?" or "Can you put them all in one bag?" or "Can you pack them all in one bag?"

At the supermarket you ask the person doing the packing to place every item in one bag. The example sentence above is quite adequate for this scenario.

The phrase 'in the same bag' used in the first request means 'in one bag' and not in separate bags. This can be done only if all the items being referred to can fit into one bag. Sometimes, items bought are put into separate bags because they can not all fit into one bag. The phrase 'in one bag' is the same as 'in the same bag'. So, you may say: Please put them all in the same bag. or Please put them all in one bag.

To put everything into the same bag is to have all of your shopping put into just one shopping bag and not grouped separately into many bags which can cause a waste of plastic.