I've had dreadful back pain on a few occasions and have had packets of painkillers stowed all over the place: bedside drawer, kitchen cabinet, bathroom. So I can understand grappling around and grabbing an old box when the newer boxes are open and elsewhere.
However. I am not a neat freak - quite the opposite.
I assume a neat freak would be more likely to be able to account for where things were, and less likely to grab an old box stuffed full of condoms.
What was he like when packing OP - was he methodical? Or did he leave it to the last minute and rush about chucking stuff into bags like I would ?
Was it an old box of paracetamol or a newer one? How many tablets were inside? If it was an old box, did it look immediately identifiable as an old box?
If it was obviously an old box then he would have known it as a historical object - the box where the old condoms live. And therefore why take it with him?
If it was a newer box, why shove old condoms into a new box - and where were the condoms prior to that?
Where does he keep the new boxes of painkillers - same drawer?
The only reason to take the box would be if he had run out of all painkillers except those, and needed a couple for the journey to the airport (where he could buy more). But if so - why not remove the condoms and chuck them in the bin at home?
And yes any back pain sufferer knows that you need to take anti-inflammatories, not paracemtamol.
Hope it's entirely innocent - and it may well be. Just really run the plausibility through your mind. You know him - can you see your neat, organised OH grabbing an ancient box of painkillers in a rush, completely forgetting about the condoms?