Juice brand that people drink in Iran. I also think it has some kind of a political or social classification reference to certain groups of people that support the regime. I have seen it appear in references made like saying "Folani Sandis Khoreh" or "Sandis Khora" and stuff like that. I am sure others can elaborate more!
historically
Capri Sun style of of package "juice" made of concentrate is the cheapest form of refreshments sold in iranian convenient stores.
perhaps a replacement for traditional yakh dar behesht, khake-shir, ab zereshk that used to be sold around the country.
in more recent years
رانی has replaced sandis as the more popular juice packaging. because it also has some fruit pulps in the packaging.
back to political vernacular.
ساندیس خور
refers to a very poor individual who is willing to bused in the by the government to a demonstration and only merely be compensated with Sandish refreshment.
Basically mocking the person for selling their soul for that cheap.
of course in recent years Sandis is merely just a symbol. typically those bused in demonstrator might receive a nominal food coupon or something like that.