I get this too, order several items together, & then it gets split up. I can see (from tracking via a/c) items are coming from different places/warehouses, sometimes from Europe, & you can't tell that before you buy. Agreed frustrating.
On Prime there doesn't seem to be the option of having items delivered together (I've tried several times, albeit not recently).
If you are not on Prime there used to be a box to ask for all items to be sent in same parcel.
If something I'm ordering shows as coming in original packing I ask for Amazon packing - (as if its a gift) as far as I remember its a 2 stage process - ask for it then click the save button (easy to forget that bit).
For a while now if item is coming via Amazon Logistics I've been shown a map (via tracking in a/c), updated every 10 secs, of where the driver is for (I think) the last 10 stops he/she has to make before they reach you.
They also put up a time slot of around 4 hours - but it can change so not overly useful.
What I'm more frustrated/worried about is the age verification on alcohol - was the subject of a previous thread here.
Amazon Logistics drivers ask to see date of birth (driving licence/passport), so they know your DOB, address & your name. Those 3 pieces of info can be sold on and lead to identity fraud. Sometimes when under pressure a driver hasn't asked for DOB but mostly they do.
My last Amazon pantry order included alcohol, came via UPS and I did not have to verify my age.
Having to provide DOB to drivers as opposed to just declaring over 18 (& looking it maybe) is to my mind over the top and dangerous given the possibility of fraud. Hasn't stopped me buying, think I should.