I always take multiple types of bait and many different colors and different scents too. You never know what the fish will bite on the day that you are there. If you don't have the right bait, right color, right spinner, flies, spoons, etc. you may get skunked. A variety is always best.
Plus, when trolling...if you don't catch anything near the surface, then add weight and go deeper until you find the zone. It's also wise to vary your trolling speed as well. SLOW is generally best (from 1/2 mile per hour to 1.5). But sometimes varying from slow to fast back to slow; or just faster and steady will work.
Another technique that many peeps don't try is making an "S" pattern when steering your boat. Turning slowly from side to side will drop the inside gear down deeper, while raising the outside of the turn gear up higher. It's another variation on depth and speed.
When these methods are used, it's a rare instance when trolling doesn't work.