Shooting photos using your camera's built-in flash can lead to harshly lit, unflattering photos, but if you're in a dark space you need something to light your subject. Try using a white balloon as a pocketable flash diffuser that you can have ready to use in seconds.
As its name suggests, a flash diffuser takes the bright "spark" of a camera flash and spreads it over a wider area, like a lampshade. This makes your photo subject more evenly lit, instead of looking like there's a spotlight shining on them. In this video from the Kuldonov Brothers we see how a white balloon can serve as a diffuser in a pinch. (You can buy an actual attachment that sits over your camera's flash, but those are usual designed for speedlight attachments, and besides, it's an extra bit of kit to carry around). I've occasionally experimented with holding plain white paper over the camera flash, and really you can try using any white semi-opaque surface. A white balloon, though, is surprisingly effective.
Simple diffuser for pop-up flash in portrait photography [Kuldonov Brothers via PetaPixel]