There are no "this column for x, that column for y" rules written or unwritten, thankfully.
Visually people expect navigation, headings, search boxes, etc in particular areas of the screen.
But to ensure accessibility you just need to make sure the whole site makes logical sense when linearised, and with no sounds or graphics, - just as if someone was reading the site out to you and you said "yeah click that link", "ok skip to this paragraph" and stuff like that.
So if each section in linear order has a heading like "navigation menu", "shop browsing area" and "shopping cart" then these are like sign posts for blind, seeing, or whatever people might be using the site.
To get an idea of how sites are when linearised, see the
Lynx web viewer, and good luck!