Deep breaths. The surgeon does this kind of thing just about everyday.
It is easier for the staff if you leave nothing with her except for what they ask for. They have to keep track of it otherwise and that can be difficult. Just let them know she gets cold easily and they will give her extra blankies. She will be closely monitored, including her temperature and whether or not she is shaking, so this isn't something that you have to worry about. She will also have an IV in which may go in her front leg. They may not even be able to put a shirt on her...
I didn't think most dogs came home casted after LP surgery anymore. Not sure that getting her feet wet would hurt a thing. And if the surgeon doesn't want her wet, there are ways around it. Plastic bag over the leg when it's wet out...
It sounds like you have everything. And because her recovery is going to be something like 8 weeks, chances are high that you'll have to leave a time or two. That is completely okay. They aren't going to send her home if she is unstable (which is not likely anyway). She should have somebody with her for a couple-few days and then she'll be good to go it alone anyway. She should be just fine.
