Hi, I recently travelled MAN to AUH to JNB with my wheelchair. Initially I only had one carry on; soft sides with handles which I hung by the handles over the chair handles. Being a bit of a shopaholic, I did some duty free shopping and carried this rather large bag on my knee. The pusher had no problems.
As flyingwheels mentions, do take care if you sling a bag over the handles, that it is not too heavy so that you don't overweight the chair and make it tip if you stand up.
Good luck. I am sure you will manage just fine.