とにかくメシ・・・といきたいところだが、その前に用を足すことにした。

・・・、。

Food first... is what I'd love to say, but I decided I'd better hit the bathroom before that.

Literal

Anyway grub... [quot-と] want-to-go place [copula-だが], its-before-に bodily-need [obj-を] relieve [decide-ことにした].

メシ 'grub / chow' is a rough/masculine colloquial form of 飯. とにかく~といきたいところ 'I'd like to just X' uses いきたいところ 'the point (where) I'd want to go' as an idiomatic framing for a stated preference that is about to be qualified. 用を足す is a euphemistic set phrase (literally 'dispatch a task') for 'relieve oneself / use the bathroom' — a very standard polite euphemism. ~ことにした 'decided to' marks a personal resolution.