A few days ago, 10 rolls of Ilford XP2 400 arrived, as I am now getting ready for my trip. Now I am having second thoughts - isn't b/w a bit unsuitable for photographs taken in summer - or, rather should I plan the project (next week is just a fact-finding rehearsal) to be done in March or October?
You mentioned in another post that this was to be done "Ara Güler style". He shot (mostly) black and white in Istanbul all year round, so no problem for you there. One characteristic of his style, however, is that he shot a lot either at dawn or at dusk. Contrast is high, shadows are deep, there is a dream-like quality in the landscape that appears in the background. This is what gives his photographs the "romantic" look he liked and looked for — much reminiscent of Fan Ho in that regards.
This is to say that summer is indeed excellent for black and white, especially if you are willing to get up very early.
That said, I agree with Ralph. I would have taken FP4+, a slower film, for this. 400 is practical, but to me doesn't give enough versatility regarding F-stop use in bright, if not harsh, summer light — unless you're OK with shooting everything at F/16 or f/22. On this matter, Huub's suggestion of carrying an ND filter is excellent, if you are going with the 400 ISO film.
Another reason to avoid 400 ISO films when traveling is the matter of the new airport scanners (there are a couple of threads on the subject), which, it seems, can damage fast films more than the slower ones.
BTW, it would be helpful if you told us where you are going.