I had a thick book as a kid, it was big too, bigger than an A4 sheet of paper, and it was full of illustrations and different short stories.
There was one where different types of dogs were all rushing to attend a party.
And there was one where a boy invented many different gadgets including a submarine which he sealed shut with a wad of gum and he met mermaids underwater.
Please help me find the title of the book!

Was it a Dr. Seuss book? The Dog Party sounds like Go! Dog! Go!

No, it wasn't it was full of other short stories. Maybe go dog go was compiled in it as well, but thanks!