Suse's Kinder Rain Poncho Is the best way to keep dry - you can wear your baby on your front or back - as there are "hidden" baby hoods under the flaps at the front and the back of this garment - you could even wear twins (one on front and back!).
I know some of you will gape at the price. But it is useful for years (from birth until whatever age your child stops needing a carry/piggyback (even 5y olds can get tired on very long hikes!).
I definately found the soft carriers I mentioned a LOT more useful than the framed carrier, aswell as being comfortable.
I even use the soft carriers in the home while I'm cooking or cleaning if my youngest is tired (he's 2y) and needs me - but I need to get things done!
I also use the soft carriers on the school run - or when I'm just nipping to the shop for bread and milk.
You can carry supplies in a waist pack - or get your partner/walking friend to carry a rucksack with bits in.
I can only wince at the though of the pain from carrying a large framed pack laden with toddler and other stuff in the onboard storage space compartments!
I think the problem with all framed carriers is they carry the baby very high on your back - (so they can look over your shoulder) - which means above your center of gravity (naturally just above the hips - where you'd carry a child piggyback close to your body) they often seat the child with some "air space" between parent and child too - putting even more strain on your spine.
For the child - often the seat in a framed carrier is too narrow - Ideally the baby/child will be seated with bum lower than knees and with full support from knee to knee under the bum. This is not easily acheived in a framed carrier. The wrap sling is unrivalled in providing proper ergonomic and comfortable support. Storchenwiege is another brilliant make of wrap sling - they're especially woven and give fantastic support.
You may need a bit of practice with the wrap sling - there are plenty of videos on the web to watch and learn from.
Storchenwiege Different Holds using the same wrap sling
The importance of leg position for baby when choosing a baby/child carrier
Back carry with one month old video
Babywearing Videos on Youtube
This is something worthwhile learning not only for hikes and holidays - but they are so useful for many situations - and make for an easier life for you!
Think of the cost of an all terrain pram or framed carrier and weather accessories - then compare to the cost of a good wrap sling and rain poncho - not too different BUT the wrap sling can be used from birth to 5y comfortably - they are compact to store and easy to carry just incase. A wrap sling also makes a great hammock, or blanet, or picnic rug or toddler swing....it is so versatile.