But that's exactly the opposite of what universal basic income should be used for (waste on excesses/luxuries before basic needs are met).

I grew up in a household with relatively little income, where you barely have enough for food and housing. I cannot imagine being in that situation and spending much on random next day delivery luxuries from Amazon - you literally would starve. The first thing on my mind would be upgrading from beans and rice to other foods, etc... that sort of thing.

Buying into luxuries only really occurs when you exceed the ability to provide for basic needs. Basic income if implemented will be tuned to provide basic needs, not luxuries -- the only time I see this changing is in a distant future post-scarcity economy.