The right accessories can really complete an outfit and make it more individual and unique too. You might choose to make your own zombie clown outfit and then purchase some important pieces like the wig, a mask (so you don't need the bother of putting on make-up) and other accessories which identify you both as an undead creature and as a circus performer too.
If your character is a killer, what weapon will he be carrying? You can purchase pretend weaponry like the knife on the right which is blood-stained. Your guy could carry a knife, a cleaver or just a random thing he picked up on his travels like a thick stick.
These performers often have goofy accessories like this squirting sunflower. How gross would this be if you colored the water with red food coloring to look like he is squirting blood. But don't squirt it over anyone's clean clothes.
Are you going to paint your nose red or buy a red nose? How did your character die in the first place? If he was shot, does he have a bullet wound anywhere? Or what about a stab wound which has become infected. These effects can be achieved with latex accessories. An easier option is to wear a bandage somewhere and give it a fake blood stain.