A chef's delight (barrel) flatpack can be made at a workbench (Steel framed bench or better) in the workshop of a player-owned house. This requires 48 Construction and 54 Cooking, uses 3 oak planks, 2 steel bars, 8 Chef's delights and gives 224 experience. The flatpack can then be used on the beer barrel hotspot in the Kitchen room while in building mode. This requires no Construction level and gives no experience.
The cost of making and selling a chef's delight (barrel) flatpack from scratch gives a profit of -46,990 coins.
After completing the hard Fremennik achievements, they can also be traded to Advisor Ghrim in exchange for 109 coins being added to your kingdom's coffers in Miscellania. See Flatpack: Miscellania reselling for details.