Yeah...it did get to...if it fit in it went...they often had me walking with all sorts in there to see if any object would fall out. There would be fuck stops not rest stops on the walk that's when whatever was in there would be changed too. So, carrying a kitchen sink would be a bit impracticable.
If we had arranged a pic nic walk we both made up a pic nic box plus something unusual to play with. This also applied to whomever else he had, unknown to me, invited along. I only ever found out if that was the case when he met me at the bus stop layby. He knew that I found the not knowing excitingly erotic. Seeing others in tnhe car with lunch boxes I was only too aware that there would be some odd things about to be worked into me...joy of joy.
In the late 60's my then boyfriend Tom ensured that I too enjoyed similar country walks or pinnics. The only difference was that if my little towel was out I had to be naked for him within ten minutes of getting in the car, no matter who else was there and that I had to remain so untill we returned to my estate car park.