Big or small dogs can use them with no problems - sometimes I put them on the floor of the van for the bigger dogs. They don't all appreciate it, but some do. I don't take them on a walk as they are not very comfortable to hold and it means one hand is 'wasted', I use a smaller more portable carrier.
Bit worried about Scarlet licking her lips while looking at Max...
I use my water bladder in a small backpack, attached to the back is my powermonkey explorer, which charges while in the sun and I can use it to charge my mobile phone while I'm out. I can't find the photo now, but I'm sure it can be imagined.