Poor people are disproportionately likely to shop in-store rather than online because they're vastly more likely to be unbanked (i.e. no credit card) and be low-education.
I'd hazard an educated guess that the percentage of income spent by the poor online is tiny. Both because the above factors and also because the majority of spending for those group is going on rent, groceries, vice (cigarettes and alcohol) and transport which aren't commonly bought online in any case.
Not to mention that there's a significant portion of people who really are so poor they aren't online. I understand that the HN community may be sheltered in many ways from a world where people can't afford a computer or Internet access, or a smart phone, but that world exists, and is not as small as we'd like to think. (I grew up in a family where a trailer home with a broken-down Pinto in the yard would have been a step up ... for some family members, very little has changed)
> "because they're vastly more likely to be unbanked"
This is not true in the US, where your debit/bank card is also a VISA/MasterCard fully usable online. Even people with zero credit can easily spend money online. If you have a bank account in the US, there are effectively no barriers to spending the money in it, online.
Walmart and K-Mart are "fixing" this with free payroll check cashing and rechargeable debit cards. One uses MasterCard and the other uses American Express.
I'd hazard an educated guess that the percentage of income spent by the poor online is tiny. Both because the above factors and also because the majority of spending for those group is going on rent, groceries, vice (cigarettes and alcohol) and transport which aren't commonly bought online in any case.