I've mentioned 口 (kǒu/mouth) before, in my post on 四/sì/four. In that post, I was mainly concerned with its use as a radical (of which more below). 口 does appear on menus in its own right, though, perhaps most notably as 口水雞 (kǒu shuǐ jī), or "mouthwatering chicken", a Sichuan cold dish of poached chicken dressed with a spicy sauce. I've also seen 口水兔肉 (kǒu shuǐ tù ròu), which I assume is the same thing but with rabbit (兔/tù) instead of chicken.
Another manifestation of 口 is as 青口 (qīng kǒu), literally "green mouth", which refers to a type of mussel. You might see this as e.g. 豉汁炒青口 (chǐ zhī chǎo qīng kǒu/stirfried mussels in black bean sauce).
I've also seen 口條 (kǒu tiáo), which literally translates to something like "mouth strip" — I think this means "tongue", but it was on a Chinese-only menu, so I don't have an English translation to compare against. The specific dish was 紅油口條 (hóng yóu kǒu tiáo), i.e. 口條 in chilli oil ("red oil").
I admit to remaining somewhat confused by a dish listed on the takeaway menu of Sichuan Restaurant in Acton — in English it's number 132, "fried beef with chilies & peppers", while in Chinese it's 口口香牛肉, which as far as I can tell means something like "mouth mouth fragrant beef". I would dearly love to know what's going on there.
Finally, 口 is used in the transliteration of "Coca-Cola": 可口可樂 (kě kǒu kě lè). You might see this on the drinks (飲料/yǐn liào) section of a menu.
Here are some characters that use 口 as a radical:
|單||dān||individual/list — used in the word 菜單 (cài dān), which means "menu" (and which you may recognise from the icon I use for this series)|
|品||pǐn||product/commodity — often used on menus to indicate the dessert section, as 甜品 (tián pǐn), literally "sweet things"|
|吃||chī||to eat — often used on menus to indicate a "snack" category, as 小吃 (xiǎo chī, literally "small eats") or 小吃類 (xiǎo chī lèi, literally "small eats category")|
|各||gè||each/every — sometimes used on menus as 各式 (gè shì) to indicate that an item is available in multiple styles (e.g. red-cooked, with black beans, with XO sauce, etc)|
|味||wèi||flavour/taste, as in e.g. 怪味兔 (guài wèi tù/"strange-flavour" rabbit)|
|咕 and 嚕||gū and lū||used together on menus as 咕嚕 (gū lū) to indicate a sweet-and-sour dish, e.g. 咕嚕肉 (gū lū ròu/sweet-and-sour pork)[see footnote]|
Footnote:  As sung points out in comments, this is a Cantonese name for this Cantonese dish which is often mistakenly transliterated into Mandarin as 古老肉 (gǔ lǎo ròu/"old-fashioned" pork); for example here. Update, October 2011: see Fuchsia Dunlop's article on sweet and sour pork for more on etymology.
|口:||kǒu||radical 30 (口)||Cantodict||MandarinTools||YellowBridge||Zhongwen|