What can I use if I don't have solder flux?

I'm just curious, what can I turn to as an alternative if I'm short on solder flux? Is there any common household item or perhaps a professional substitute that could serve the same purpose? I understand flux is crucial for ensuring a smooth and strong solder joint, but I'm wondering if there's a workaround for when I'm caught without it. Would it be safe to attempt a solder job without flux, or would the results be too unpredictable? Could you suggest any techniques or best practices for soldering without flux, just in case I'm in a bind?