The speaker sits at home on an ordinary night, feeling both grand and a little ridiculous. The title's phrase, "high on the hog," usually means living in luxury, but the actual meal is only bread and cheese. That gap is the joke, and also the point. The speaker's head is "full of money," so he is rich in daydreams or worries about cash while his plate stays plain.
The comparison in the first stanza is the most striking part. He is "high and fat as a parliament / nobody cares for," which suggests puffed-up importance with no one paying attention. A parliament that is ignored still looks impressive on paper but has no real power. The speaker seems to see himself the same way: bloated, self-important, and unnoticed.
The mood is wry and quietly lonely. There is humor in the self-mockery, but the short, flat lines leave a small sting underneath.