If you want to know what quests to avoid, I can definately tell you. Very first step, get the Wooden Master Key to open up the families with the Melluzine Key, Chaos Stapler, and Evil Liquor. The quests to avoid are Malnutrition, Good Taste, and Armageddon. Good Taste can be finished after getting at least one Melluzine Key, one Chaos Stapler, and two Evil Liquors. Malnutrition should only be completed after obtaining all c5/6 quest items, mainly because it has the Project Finisher (Deck of Cards and Motion Twin Survival Kit families opened with these, those are a big NO), and the c5 Chocolate Mousse (crap that gives 1 pt).
For effect items, don't do Armageddon until getting one BoS and BoM. The Green Beer Mushroom dosn't have to be gotten before doing Armageddon. Same goes for the two Gon Ga Joras. After that's done, open Armageddon and once you also have one Chouros Hair, three Tuber's Bags, one Golden Mushroom, and one Pioupiou,(in addition to one Manda and one Octopus in Ink) you can complete Malnutrition. The reason I keep Malnutrition off to the side for so long is that it leads to the Ace of Diamonds, Hearts, Green, and Purple Pearls. I view those items as undesireable waste because they are part of no quests, and they only reduce the odds of obtaining quest-related c5/6s.
Ok, so the items I avoided for Good Taste was the

, nothing else. The

is
WAY too common and the Bobble Canes are too good to avoid. For Armageddon, I avoided the

and

. For Malnutrition, the quest most critical to not complete, I chose the Bizzare and Strange Liquids. I am still avoiding them today. Not on this account, of course. It's just a coincidence that my brother never unblocked them.
If you ever get one of the banned items accidentally (

these are just the ones that I chose, it really doesn't matter as long as they're uncommon and you need a number of them), it's OK if it's just one. Otherwise, close the game without saving. You can do that by simply closing the window or tab.
Wow, that's a very simplified versoin of the thread I made, but next is my Tower of Greed. I went to the ToG thread, and the link led me to a very strange website, some kind of forum. So, here it is in text:
1 Book of Mushrooms
2 Books of Stars
2 Chouros Hair
1 Tuber's Bag
1 Green Beer Mushroom
2 Gon Ga Joras
2 Melluzine Keys
2 Evil Liquors
1 Chaos Stapler
No c6s, yet. I also missed a Croissant once, but I'm just glad it wasn't a quest c5.