Red maggots, worms, sweetcorn and, sorry to say, boilies, in that order, with a lot of groundbait high in attractant but low in actual food.
Unfortunately everything else likes maggots, worms and sweetcorn as well, of course, so places where there's a large number of silvers is where the boilies come in.
I've also had good success with snails in the past and the tiddlers seem less interested, but they're incredibly difficult keeping on the hook or hair as they're so fragile and break apart the minute you look at them, so I've not really tried them lately. They're also quite expensive these days (dirt cheap when I was using them over 20 years ago), so unless you live somewhere where you can get some "from the wild", they're not really an option.
I've never actually tried mussels. As far as I know only one of the places I fish for tench actually has mussels in it, and I have heard that mussels are the type of bait that only work in places where it's already a naturally occurring food source (as alluded to by seth49). That may be apocryphal, though.