Strange rocks obtained by training Cooking are part of the Dahmaroc statue. Two Strange rocks from each skill are required to complete the statue, which can be built once per week. Strange rocks may be stored inside a statue collection bag.
Shrimps are a good choice as they are cheap and you will stop burning them at level 33. By tying this into the fishing activity, chefs can cook whatever they have fished. To minimise burning, use cooking gauntlets if you have them available and use cooking ranges instead of fires. The cooking range in the kitchen of Lumbridge Castle has the lowest burn rate of all, but is not as convenient for a bank as Catherby (or the Cooking Guild for those with Varrock armour 3) and so is slightly slower overall. If you have no chance of burning the fish you are cooking, the permanent fire in the Rogues' Den is useful as the bank is only a few steps away.