Chips, nuts, and berries all sank to the bottom?

All of these goodies tend to be much heavier than the batter of most cakes or bar cookies, so it’s a simple matter of gravity taking over when you find them all clumped at the bottom. However, by coating the mix-ins evenly in flour before adding the wet ingredients in, you stand a fighting chance of keeping them distributed throughout. If they still fall and this bothers you, you can instead try sprinkling them on top of the batter once spread in the pan, so that they may ultimately end up in the middle as intended.