Aftercare is the term used to describe any sort of care that is administered after a scene is over. What kind of aftercare is needed is different for different people. In the context of the sexual practice of BDSM, aftercare is the process of attending to one another after intense feelings of a physical or psychological nature relating to BDSM activities.
BDSM experiences can be exhausting; and drain the participants of mental, emotional or physical energy. As a result, one or all participants may require emotional support, comfort, reassurance, and/or physical tenderness. Along with this, he or she may experience everything from an exhilaration to traumatization.
After a session of play most people include a time of "debriefing". In the "debriefing" allow time, whether your the dom or the sub before opporating heavy machinery. Especially if it is your first scene, do not plan on driving afterward especially if you will be on the receiving end of the play. If you can't play in your own home, make sure you will be able to stay for at least an hour after the scene is over, maybe longer depending on how the play affects you.
After a session it is likely that you'll be hungry, thirsty and possibly cold. Scenes are typically long, so by the end you're probably going to be very hungry and thirsty. You'll probably be exhausted once the scene is over, so you want things like cut up fruit or sandwiches that can easily be thrown together on hand. Many people get cold as they start to come down from a scene, so keep a blanket close by that you can wrap around you if you start feeling cold. A blanket will also be useful if you are someone who needs cuddling after a scene. Your dom/top can wrap the blanket around both of you and it will make the cuddling feel even better (at least it does for me).
Remember, that not just subs need "aftercare". Just because after one scene you were immediately able to jump up and go about your business, that doesn't mean that will always be the case. Different activities trigger different reactions, so one day you might be fine with just a kiss on the forehead and a hug, and another time you might need to be held for a half an hour. This is why that debriefing time is always something that should be included for everyones health, both mental and physical.