Sorry, as I said I'm on vacation at the minute, so my replies have been, & will be, far & few until about 7th or 8th of September.
You need to use an additional condition &/or setup a combination condition. Or ideally just use a value instead, which has a default value of 0 (0 for bag not taken), then when bag is taken set value to 1 (1 for bag taken) & then you query if value is 1 in the at begin of scene action. Then after you've performed whatever action you are talking about to get the dog to stop following you into each scene just set value to 2 along with the stop chase action part.
P.S: based on the middle screenshot you posted: you need to add another end if action part onto the end, but to be honest, you didn't actually need to add the: if condition 'sac dispo?' bit as the else on its own was sufficient enough. Because you added the additional if, you need 2 end ifs. Always the same amount of end if as if.