Just done 15 days to mull and western isles with 7 month old (and his 2.5 yr old brother) in hightop t25.
Parcel shelf bed for baby (do a search for link or come back to me for details) - both slept like a log on it!!)
Bottles - if your baby normally has warm milk try them on room temp before going - many babies don't mind - powder mixes fine - both of ours have have it cold from getting off the nipple.
STAR TIP - sterilising bottles = use Miltons tablets (15 mins and 5 litres of cold water and a tablet is all you need - oh and a bucket/tub) - works a treat
BABy CARRIER (beg borrow or steal one) - you can get on with the chores whilst entertaining the little un.
If you can take the buggy (we have a Mountain Buggy and it does go up mountains... - then a good place for them to fall asleep on the beach etc.) we strap ours behind the pass seat then chuck under the van when camping
As for disposing of nappies - it
is possible to use real (non-throwaway) nappies - use laundrette for washing or handwash in a bucket and hang up from someones guy ropes (prob best to ask them tho

).
Fav comforter is a must - and stick to daily routine (nap times etc.) as best you can - it really works and makes for a more enjoyable time for all
Baby seats - check compatibility - there
are lapbelt compatible seats out there (again pm me for a list if you need)
Sun cream and sun hat(s) as babies skin really needs protecting
Feeding solids - think about how you will feed them - you could use the car seat (but can be messy) - try to find a booster seat with tray (plastic moulded thing with a clip on tray) - like a low level high chair - allows you to feed them anywhere from the floor - to the field to the seat (again if you need more - come back to us). - Also tray is good for letting them play with toys whilst you shovel the food in.....(if you have a BUMBO - you can get a tray for it)
We found having
curtains made from blackout material really helps - in North of scotland where it is thinking about getting dark at 1045 at the mo - they really make a difference when they are going down at 7pm.
Calpol, thermometer, babies "red book" (med details), teething powders (if 5 months onwards)....
Make sure you have lots of places to hang and dry out bibs and face cloths.
Finally - DO IT - we are just back from a great trip - I am sure the little uns enjoyed it - even if they don't remember it when they are 25!