Food preparation forbidden on Jewish festivals includes these forbidden melachot:

• Preparing soil for planting (choreish)
• Causing plants to grow (zorei’a)
• Harvesting (kotzeir)
• Gathering (mi’ameir)
• Threshing (dash; such as milking a cow into clean container or squeezing juice for drinking)
• Winnowing (zoreh)
• Selecting (boreir) (for exceptions, see Introduction to Jewish Festivals: Selecting/Boreir)
• Grinding (tochein) (Grinding may be OK with a shinu’i; ask a rabbi for specific cases)
• Sifting (merakeid).

However, you may do all food preparation necessary for baking or cooking food for that day--from kneading dough (kneading, or lash) to cooking and baking (ofeh) from an existing flame.