Flash memory is not magnetic memory and is
not affected by magnets. This covers your SD
card and your firmware. The vulnerability issue
is with the actual electro-mechanical devices of
which there are many inside your gear. Keep
the naked magnetic "grabber" side of the quick
connect away from your gear during transport.
As to magnetic closures for bag flaps, popular
powerful disc magnets should not be stitched
into flaps as-is. The emanate a powerful field
from both of their flat surfaces. It is safer to
create magnet that emanates a powerful field
from only one side, IOW only in one direction.
The proper precaution is to set two discs onto
a strip of steel, where they will cling, but epoxy
them anyway. Set them with opposite polarities.
The strip of steel is their keeper on one side but
the other side has a powerful field. Stitch this
assembly into the bag with the field pointing out
and away from the interior of the bag. A steel
strip stitched into the flap will cling to the hidden
Placing magnets with mutually opposite polarity
on the strip will provide a tighter grasp on the
steel-loaded flap vs having both magnets facing
the same way. This allows you to use weaker
smaller magnets yet still have a powerful hold
for keeping the flap closed. Opposing polarities
also bend much of the magnetic field into an arc
between the N-pole of one disc and S-pole of its
partner. If both discs were mounted with to the
strip with like polarities,the field would not arch
but would emanate straight out from the open
["unkept"] side of the pair of discs.
Essentially, adhering the pair of discs to their
steel strip at opposite polarities creates a horse
shoe magnet. OTOH, adhered with like polarity
you have bar magnet. Despite lacking the horse
shoe shape, or bar shape, Very importantly for
safety, the shapes of their fields will be as per
those horse shoe or bar magnet shapes.