If your city doesn't have bike lanes, it's up to every car that passes you on your bike to determine how much space to give you. Despite tough new passing laws in some states, they often still suck at it. Cyclist Warren Huska solved this by strapping a pool noodle to his bike.
The noodle, as you can see above, sticks out a metre or so to the side of the bike to give drivers a visual indicator of how far away they should stay. This concept isn't entirely new. In Europe, reflective spacers are common and cheap. These circular flags stick out to the side so drivers can see how close they're getting.
Of course there are downsides to the pool noodle technique. They're not exactly designed to mount to bikes, so if you don't attach it properly, it could come flying off in traffic. It could potentially get caught on other objects or cyclists if you frequently use bike lanes. You'll have to judge for yourself whether it will work for your cycling habits.
Most of all, it just looks silly. However, as we've learned before, being silly doesn't negate being useful. As Huska himself puts it, "I'm unconcerned about looking good...I'm concerned about my safety most." If you're worried about any of the above concerns, you can always buy a proper reflective spacer, but if you go the pool noodle route, it's still probably safer than trusting the visual judgement of every driver on the road.