Take antibacterial hand wash gel- there doesn't seem to be any taps/sinks next to toilets at all.
Luckily, didn't have any stomach problems but be prepared with a good personal first aid kit. I seemed to go through quite a lot of anti-inflammatories! No blisters although others in the group did, I just had sore feet by the end of some days.
I found having a effervescent general multi vitamin tablet good- the diet was a little limited- very little fruit. The tablets also good for flavouring water!
Be prepared for some poor hygiene- I found it quite difficult to deal with for the number of consecutive days. Wet wipes, wet wipes, wet wipes!
A metal water bottle is a good idea as can be used as a hot water bottle (it gets very cold at night even in down sleeping bag!).
A scarf/buff that can wear as a face mask- roads in Kathmandu and some parts of the circiut are very dusty.
Be prepared- this is a long walk. Make sure it is within own capabilities, do some practice hikes. I would like to feel I was a "walker" walking regularly in Scottish hills but this trek is a big undertaking and was harder than others I have done. After many days of walking, the last 2 days are tough (big ascent 1800m/descent- 3600 steps!!) after 15 days of walking- it was hard going.