An asgarnian ale (barrel) flatpack can be made at a workbench (Wooden workbench or better) in the workshop of a player-owned house. This this requires 18 Construction and 24 Cooking, uses 3 oak planks, 8 Asgarnian ales and gives 184 experience. The flatpack can then be used on the beer barrel hotspot in the Kitchen while in building mode. This requires no Construction level and gives no experience.
The cost of making and selling an asgarnian ale (barrel) flatpack from scratch gives a profit of -4,070 coins.
After completing the hard Fremennik achievements, they can also be traded to Advisor Ghrim in exchange for 86 coins being added to your kingdom's coffers in Miscellania. See Flatpack: Miscellania reselling for details.