Hi,
"Yesterday, I went to my favourite cafe and I ordered the usual: a vanilla latte... (...) ...Sometimes, I'll order a coffee cake if I'm feeling a little hungry.
Is it correct?
"Sometimes, I order a coffee cake.."
Yes, there's really no difference in this context.
(Usually, we speak of some coffee cake rather than a coffee cake. They cut a slice for us.)
Best wishes, Clive