IKEA UK is currently selling "student boxes", which is grab-kit thing for new kitchens.

in the store, it has a gnarly 16-square data matrix barcode that reads:

9100005240802984743012405013758130124060143992301240601439923012408707770030124050525642301240502583233012405025832330124000081534301240902022683012400034300330124080258915301240802589153012400031894230124000318942301240302589133012403025891330124030407814301240402784683012403010297430124070455087301240005452183012403052193730124060521945301

all ikea items have a 8-digit article number. with some visual pattern matching, it seems like:

• 9100005 240 is the prefix for "heads up there are a load of item codes coming up in this barcode". there are 24 items in this box, so maybe the 24 means that.
• the first item is 80298474, a pot
• each item is then separated by 301 240
• the last item is 60521945, a colander, and
• the suffix is 301

given the item separator also has '24' in it, i can't tell whether this just a coincidence or they also indicate the length of the item list; so maybe don't compile a barcode that has 15 blahajs for the funny just yet.

edit: thankies for the replies, it seems like i have not occam razor’s hard enough — 240 might just be a generic “item code begin” separator (and 301 being a generic “item code end” separator)

update: found another “student pack” from ikea, with fewer items this time.

910000524070429003301240105798683012404038125330124090460573301240303565793012406056543030124010606051301240205038873012402031707930124010056770301240004285493012403055360730124040295439301

so, many commenters in the original post is right:

9100005 is a common header indicating a multi item barcode
240 is item start
301 is item end, with no checksum or list length information

this does mean crafting a data matrix barcode for your whole cart is theoretically possible, but it will look incredibly suspicious to staff if one does not scan any items at the checkout but instead a big funny data matrix on a mobile device  

i wonder whether the “checkout via app” is build upon this, time to find out next time i head to ikea 

anyways, 10% off coupon code for your next IKEA UK shop!

THAT WILL TOTALLY NOT ADD 16 GREEN GLEEP GLORPS INTO YOUR BASKET

@kuriko get it printed as sticker and put it over some other random barcode
@lea hmmm I would need a label printer that can print bitmap or supports data matrix codes natively, that sounds like specialized equip-
@kuriko it is slightly different, I guess the code is for the card tied to your account