Simond9x: 26d uses the same ‘meal’ that appeared on last week’s puzzle, if that’s any help, and then is missing the same ‘piece’ that was used in that puzzle. ‘Of’ is then a single letter on the end, and the first letter is the extra one.
16d is a nightmare. First three letters is the pool, then you have 250 (mediaeval Roman numeral letter, one of two to choose from) and the letter for Roubles ‘hidden’ (removed from) a very obscure six letter word meaning ‘a compartment of vaulting’, which includes the extra letter.