Peanut butter and marmite are an excellent combination. Definitely need to go easy on the Marmite if you are a neophyte, though.

Plain white toast is usually the preferred conveyance, though things like challah or Japanese milk bread are also pretty good.

The “Scottish loaf” referred to might be this, as contrasted with the more posh “pan loaf” https://en.m.wikipedia.org/wiki/Plain_loaf