I am only familiar with the abbreviation of kilogram as kilo, and this is indeed pluralized as kilos. I have heard mega and megas from foreigners but they strike me as ungrammatical, as does nano from nanosecond (why not for nanometer?). Here’s what I found in the Corpus of Contemporary American English:
All the incidences of nanos were references to one of the following:
- iPod nano
- A surname Nanos
- In science fiction, references to something like nanorobots
So, nano(s) is not a commonly-used abbreviated form for nanosecond (or nanometer)
As for megas, the only examples in COCA were three uses as a name, and one use in science fiction:
So after the Port dome went up they built this lean-to partial dome that tilts up against the Port dome like a crescent cupping a bigger arc: the Curve. It was supposed to be just warehouses and megas, not living space, so they didn't attach it to the Port dome very well and now the Curve pulls away from the Port dome a little more every year, and a little more gas and garbage falls into the Curve but nobody seems to give a damn.
It’s unclear from even this much context what a mega is, but I’m pretty sure it’s not a megabyte.
I checked also for uses of gigas for gigabytes but all the gigas in COCA are species names, where it presumably means “very large”: Strombus gigas (a sea snail), Crassostrea gigas (an oyster), Angelica gigas (a flowering plant).
So, in conclusion, don’t use mega as an abbreviation for megabyte. I understand this is common in some languages, such as Spanish, but it is not used in English. Use instead MB as the abbreviation for megabyte. However, kilo for kilogram is perfectly idiomatic, although in American English, the things most often measured in kilos are cocaine and heroin. The top 10 most common collocates for kilo are: cocaine, hundred, per, five, heroin, fifty, weighed, pounds, ten, and half.
EDIT: as pointed out in the question’s comments, meg(s) and gig(s) are the common used spoken abbreviations for megabyte(s) and gigabyte(s).