This blueprint will indicate how full a chest is of a specified resource using a blinking light, by varying the duty cycle of each light in proportion to the fullness. If a chest is full the light will be on 100% of the time, half full 50%, etc. Just set the signal of each light to the item you want to indicate. This can easily be expanded to as many chests as you want without adding any combinators; just add another lamp and chest, connect them as they are here, and set the lamp to the appropriate item.