Court Plaister in Emma

Harriet came to Emma to share her ‚treasures‘ of Mr Elton and one of these was a piece of court plaister.

‚Do not you remember his cutting his finger with your new penknife, and your recommending court plaister? But as you had none about you, and knew I had, you desired me to supply him; and so I took mine out and cut him a piece; but it was a great deal too large, and he cut it smaller, and kept playing some time with what was left, before he gave it back to me.‘

Could anyone explain what court plaister is? Why should a lady have this about her and where? Did the gowns have pockets large enough to carry this and other things with them all the time? What else did they usually carry with them?

Thank you :)