League-of-legends – find out the overall or per-champion win/loss ratio

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Boots are a specific case. You can't have more than one movement buff from any kinds of boots at all.

As for other items with UNIQUE passives, as long as you don't have the exact same item, they all stack on top of each other.

Apparently, there are other exceptions as well. From the wiki:

Unique effects that do not cumulate among differents items include Movement Speed effects from boots (only the best effect applies), proc effect of Sheen, Lich Bane and Trinity Force, and the mana gained from Tear of the Goddess, Manamune and Archangel's Staff.