Brown Mushrooms are one of the best foods for long trips. They provide one of the highest regeneration seconds per ounce eaten, making them very useful to mages in hunting places without food. These are not only lighter than white mushrooms, but heal more per gp spent buying them, so its not only more efficcient, but more cost effective to spend the same gp on these you would on white mushrooms. Also it's the best food obtainable in a shop. 100 brown mushrooms weights 20 oz. and will last you for 7 h 20m.
<spoiler> Can be found at daily spawns in a Rotworm cave in PoH, and Dusalk's Troll Clan Cave east of Dwarven Bridge: File:Brownmush.JPG Can be obtained through the Steal From Thieves Quest </spoiler>