Writing every day is probably one of the best practices you can develop as a writer.
Even if everything you wrote on one specific day ends up being journal fodder, it is about habitude. If you are lucky, one line you have written will end up in a poem or story.
Keep your journals,
even the ones used up, because you never know when you might come across a line or even a phrase previously written that works well in a work in process.
Another aspect to keeping and returning to those journals is you might take a phrase out of the context in which it was originally written and drop it into a new country, suddenly finding your way to the water in the midst of the desert.
Just notes—not a poem—and yet, lift two words from your notes and let them muscle their way into a scene to see what happens. You’ve got a nature scene in your journal going nowhere. Carve out the phrase about a warbling bird later and place it at a truck stop, inside a trucker’s cab. Take your rattle in the throat description of illness and slip into a character description of a story.
Keep writing in those journals even when you feel like you are leading blindly. Your blind guide could end up as Fisher King allusion in some later project. Don’t worry about trying to be poetic or categorize writings in your journal, just continue dropping those words on a page. Guaranteed that at least some of your combinations will end up in a form in which you and others will wonder at your juxtapositions.