I found something appropriate at Office Works. Not an actual LAG bag but it did the job.
Post Offices also sell travel cabin liquid containers(4) in a bag for $9.99 but that may be more than you want to spend.
Thanks Buzzard and Boca, good ideas. I am at LAX leaving in the morning. I had in mind more a budget of a couple of cents for a disposable resealable bag. No doubt I can buy a box of 500 for a dollar or something like that, but I'd prefer to avoid the waste. For instance, at BGI one year security had an arrangement/scam going with the adjacent duty-free shop: they'd send you there to buy a single bag for $5.
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Altenatively, you could just buy a box of large zip lock bags at a supermarket. Maybe a box of 20 for $5.
That's what I do. I buy the higher quality ones like these: https://www.amazon.com/Ziploc-Slider-Storage-Quart-Value/dp/B00HXCNRZ8/ref=sr_1_4_a_itAltenatively, you could just buy a box of large zip lock bags at a supermarket. Maybe a box of 20 for $5.
... Never been through a checkpoint anywhere in the world where they've complained either.