What can I use for homemade flux?

As a hobbyist in electronics and DIY projects, I'm often in need of flux for soldering purposes. Given the current market situation and supply chain issues, I'm wondering if there are any household items I can use as a substitute for commercial flux. Could you suggest some common household items that I might already have at home that could serve as a decent flux alternative? Also, would it be safe to use these substitutes in terms of their chemical reactivity or potential harm to the soldering equipment? I'd appreciate your insights on this matter.