Fully baked yam chips does not keep well in the fridge as it becomes soggy over time; and dries out when warmed. On the contrary, frozen raw yam sticks will keep well in the freezer. Toss in butter or oil with salt and spices. Freeze in a single layer first to prevent clumping, then pack into a ziplock bag and return to the freezer. When you are ready to eat, just place the frozen yam chips straight on a baking tray and bake.