Reply posted for DVM2008.
I posted this in another thread, but since you asked directly what to put in a kit, I've copied it below. In addition to the kits described below, in the car I carry TP, garbage bags, and a 5-gallon bucket (most restaurants have plenty they'd be glad to give you and they're more comfortable than you'd think). I live in the desert so there aren't any woods to crap in or leaves to gather (um, nothing but cactus, ouch!), and I commute over 80 miles to work, so the bucket is important even though I have rarely had to use it.
One
of the things that's helped me the most is having an emergency kit with
me at all times. Actually, I have several levels of kits. One I carry
on me when I have intense symptoms which contains kleenex, individually
packaged handi-wipes, and a couple compressed towel pills that expand
into a washcloth when you add water. There's a slightly bigger one in
my briefcase and golf bag that has a change of undies, a plastic bag,
and more clean-up supplies. And I have a big kit in each car and in my
desk at work that includes the normal stuff plus a change of pants. I
have found zipper pouches to put them in such that I could have a
trusted friend fetch it and bring it to me in the bathroom, without
even knowing what's inside. These layers of preparation are incredibly
important in my sense of confidence, even though the need for them is
surprisingly rare. Knowing I have them ready allows me to live more
comfortably.