As folks start doing the advanced instances (Turtle, HoCrafting, WW, HoMirrors, Watcher, 16th hall, DarkDelving. etc) the raid leader will assume that people are ready with the needed standard supplies (or may ask).
The basic kit should contain a minimum of 10 each of travel rations (embarrassing to be summoned and not be able to travel!), food, green (morale) pots, blue (power) pots, and healing pots (wound, disease, poison, fear). The crited version is preferred - for example crited lamb with mint jelly lasts 10 minutes instead of 5 and that can make a huge difference in a fight.
Other items that are highly desirable in addition are improved battle/warding scrolls (to add 5 percent to attack and defence), a stat improver such as red tea (adds 30 or 45 to vitality) and soups to improve resistances to wounds, disease, poison and fear (the potions cure them, these soups help resist them - you can take both).
Experienced raid runners will have all these - everyone should. If you don't, you might cause the group to fail because you die or you might have to ask another raid member to share theirs - its better to have your own.
Folks will ask how to get them - make them with your crafting skills, buy them from a vendor or at the AH, or make something and swap some with a kinnie for what they make that you can't.