I'd sneak them in my big red lego case I took everywhere. Under all the instructions and base plates.
I'd snatch them under my shirt and run to the bathroom when nobody was looking, and stash them under the sink for safe retrieval. Then before we would leave, with all my stuff in hand I say I need to use to bathroom and make the transfer. Lmao diaper smuggling. Often my entire visit world be occupied with concocting a plan and waiting for an opportunity to get them into hiding in the staging area. I couldn't think of or do anything else until then.
If I knew we were going somewhere that had diapers, especially large sizes, my heart world flutter and I would be plotting about it on the car ride over, just thinking how wonderful bed time was going to be later that night. A long torturous day.
One of my first stashes as a kid had a dozen different brands. After I was in bed Id pick one to put on and a second to hold in my hands under the covers and sniff the Luvs/Pampers scent and just be on cloud 9.
I'd move very slowly to avoid making noise, and made big moves when there world be laundry running or the air coming on to mask the noises. I'd keep a candy wrapper or plastic bag near by to bail me out if anyone heard anything.