The eel bone-containing baked confectionery is obtained by baking dough comprising wheat flour, butter, sugar, baking powder and a crushed product obtained by crushing eel bone. 鰻の骨入り焼菓子は、小麦粉、バター、砂糖、ベーキングパウダー、鰻の骨を粉砕して得た粉砕物から成る生地を焼き上げたものである。 - 特許庁
If the folklore is the rationale for the custom, the food to eat on the Ox day during the doyo could be 'udon' (Japanese wheat noodle) or 'udo' (Aralia cordata), since every food other than eel is possible when it has the Japanese syllable "u" at the head of its name.
この民間伝承を根拠とするならば、土用の丑の日に食べるものは鰻でなく「う」の付くものでいいのだから、うどんでもうどでもいいことになる。 - Wikipedia日英京都関連文書対訳コーパス
It is not overstating to say that it is possible to obtain almost any kind of food needed in order to make Kyoto cuisine here: Kyoto vegetables called traditional vegetables, Kyoto pickles, tofu, yuba (soy-milk skin), fu (wheat-gluten bread), eel, tsukudani (preserved food boiled down in soy sauce), kamaboko (boiled fish paste), dried fish, dried goods, tea, confectionery, bread, sushi, and so on.
そのほか伝統野菜とも呼ばれる京野菜、京漬物・豆腐やゆば・麩・ウナギ・佃煮・蒲鉾・干物・乾物などから茶・菓子・パン・寿司まで京料理の食材はほとんどここで揃うといっても過言ではない。 - Wikipedia日英京都関連文書対訳コーパス