most providers would prefer to use their own. There are several reasons for this.  In any case, this is something you would need to know ahead of time.  Some may allow you to byo condoms, but they should be sealed in the box they came in, to minimize the chance of tampering.

Swim

because every so often we hear of a provider who forgot to bring hers.

Either is fine . . .

unless you have a something that we try and I just don't like (rare) ....then I'll switch to mine.  Many providers will bring different kinds and sizes.

It is good protection from certain misunderstandings & oversights, a few scams, & inconveniences.  I have since once a Favorite lady called me back enroute & asked me to stop & get some (offered to reimburse, which of course I did not accept).  However, since I was on the road, in a unfamiliar area I wasted time that might have been critical, and had to settle for a brand that was not my first choice.  Since then, I always have at least 3 with me.  If a new aquaintance, I bring a sealed 3 pack...  leave the excess.  If a repeat meating, I'll bring 3 from my big box.  (Current, in date, properly stored.)
Once a lady said "I have them" when I placed them on the bedside table, before retiring to her bathroom.  I said simply "I like this kind"...  

I respect a lady's right to only use products that she provides, if she so chooses.  I've never had it happen.  
Why 3?  If one should get spoiled in application or mis action need to be replaced...  we're golden.  The fact she has 3 to choose from, puts her in control again.    
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