Below are some of the most common contractions in classical Chinese:
諸 = 之乎 (In some rarer cases 諸 can also be contraction for 有之乎. 諸 can be used on its own with the meaning of "all, the class of", as in 諸侯 "the feudal lords.")
焉 = 於之 (於之 is never used; only 焉.)
然 = 如之
云 = 曰之
弗 = 不之
勿 = 毋之
耳 = 而已
盍 = 胡不 (胡 is a variant of 何.)
與 = 也乎 (Also written 歟.)
邪 = 也乎 (Also written 耶. Probably a dialectal variant of 與.)