First rule: Never break lucky blocks holding important items, if you have a item deleter lucky block you will die without anything.
It happened to me, i used a enchanted shovel, this is my most useful item, but it was deleted by one of this blocks.

About the probabilities, in the yellow blocks the trap have only a 30%, unlike useless items have a 40%, weapons have 10% and tools or bad weapons have 20%. A interesting fact is that traps never appear in purple boxes that have a 70% of useless items or glass.

The blue have food or items, the are like super lucky blocks, rumors say the super have a 70% of good items and weapons and 30% of incredible weapons like diamond swords.