RALLX

They are both quite well-traveled, although probably not at the level of jetsetters. I have only met them once before the trip so I might have made a huge leap of faith in hiring them for overseas trip. There was no sign of this during our first meeting and I thoroughly enjoyed my time with them. Since I am relatively new in hiring providers, I am unsure if I have the right expectation (that providers should be well-prepared for the trip without me needing to supply them).

They are both quite well-traveled, although probably not at the level of jetsetters. I have only met them once before the trip so I might have made a huge leap of faith in hiring them for overseas trip. There was no sign of this during our first meeting and I thoroughly enjoyed my time with them. Since I am relatively new in hiring providers, I am unsure if I have the right expectation (that providers should be well-prepared for the trip without me needing to supply them).

I have hired two providers for overseas trips before and both did kind of ended on a sour note to me, for the same reason. Both providers seem unprepared for the trip and I ended up spending quite a bit to buy what they needed. With the first provider, we went to UAE but he brought mostly jeans, rather thick tops, and forgot to bring a shaver. With the second provider, we went to Paris over Christmas but his shoes were not suitable for winter and his jacket was too thin. He insisted on buying a specific brand of shoes, only to end up being unsuitable for winter still, and needing yet another pair. He also expected me to buy gifts such as perfume, sweatshirt, cap for him.
Is this common and expected, or are they taking advantage of the situation and I am just being plain unlucky?

Thanks for giving this perspective as a provider. I am usually very obliging as I do not wish to look miserable. Unfortunately I would have my feeling bottled up and the sore feeling lasted at the end of it. It is also hard for me to talk about expectations beforehand, it made me feel very calculative. But I think that is the best way forward and I have to try doing that.

To be fair, everything else was good and well. But I am hesitant to continue my engagement with them because of this. Indeed I should have discussed what expenses I will and will not cover before the trip.

I question how much common sense these two providers have, regardless of how experienced they are (or aren’t) with international travel.  Even if I had never left the US, I’d like to think I have enough common sense to google “weather Paris winter” or “weather UAE summer” before packing.

For that question: Like, duh! Yes.
The events seem like the result of a communication problem. As much as some providers want to milk a trip as much as possible, they might not have known exactly what to pack or wear. I wonder, with all the preparation and logistics that such event takes, why weren't attire and expectations about expenses during the trip discussed prior to leaving? That doesn't look like an unreasonable conversation to have in preparation.
Traveling to the UAE does require a little bit of additional information, just like traveling to certain other destinations. Also, in my experience, when certain level of elegance and attire is required/expected, it has become a need to explain to people what they should wear, and even with that, some don't get it.
I am in no position to finance such a trip, nor am I single/free enough to do so, which means that this is just speculation on my part. I'd include attire, expenses, gifts and/or other extras in the discussion before the trip, so there is an understanding of expectations. They are in the business of pleasure, so I imagine that they will do just like travel companies do, continue charging for everything that happens along the tour. That should not be a surprise (IMO).
I hope everything else in the trip went well (meaning, they didn't embarrass or dissed you).
 

That's how they trap you, but that is also your mistake. 
Sometimes when big jobs come along it is tempting to move from our normal boundaries.  While this client may be kind and generous in some ways - he at best has issues with the client/provider dynamic, and at worst is trying to get more for nothing. And the deception about the uber in order to leave you stranded in another city, what a frightful and actually scary way to behave. 
When these situations arise and people are negotiating big trips, it can be hard because you want to be flexible enough to land the big gig, but also you have to be able to walkaway afterwards (or during) feeling devalued. We have to be able to say "my daily rate is XYZ", and what happened to you on this trip is why. You need to be able to walk away from a negation. I personally price my long trips quite high because the reality is, being 'ON' 24/7 is draining, emotionally, physically and very taxing. 
Having said that - @RALLX If i was making an international trip with a client and forgot to pack my shaver, I would hope my client didn't make such a big deal of it. I have forgotten things like that. But I also wouldn't be so rude as to insist on certain brands and so forth with clothes. Good luck for your next trips and although everything should be discussed first, it is normal that a provider is not out of pocket for the trip. So drinks/food/activities are covered by the client. If the provider wants to buy themselves something while they are away, they can, and if the client wants to buy the provider gifts - they can. Gifts are never to be 'expected'.  Not by anyone with manners anyway.  

To be fair, everything else was good and well. But I am hesitant to continue my engagement with them because of this. Indeed I should have discussed what expenses I will and will not cover before the trip.

Thanks for giving this perspective as a provider. I am usually very obliging as I do not wish to look miserable. Unfortunately I would have my feeling bottled up and the sore feeling lasted at the end of it. It is also hard for me to talk about expectations beforehand, it made me feel very calculative. But I think that is the best way forward and I have to try doing that.

To be fair, everything else was good and well. But I am hesitant to continue my engagement with them because of this. Indeed I should have discussed what expenses I will and will not cover before the trip.