Yes i known that i can carry the bag, i can also walk to work and walk to the TV to change the channels! This is not a project i want to do because i am lazy (cough: i guess i am, but innovation is made by lazy people!)
This is a project i want to do because it is fun and challenging -> everybody can make a led blink........
And it has been done: http:// http://www.youtube.com/watch?v=_0XwJCllGnY
Problems with different sensors:
IR -> can be disturbed by the sun
Maybe some kind op blinking IR transmitter and the receiver should detect that "code" - and the direction could be 2 (or more) receivers separated by a plate parallel to the straight forward direction -> so that if the left receiver sees the signal, but not the right one the bag has to go left!
But my "worry" is that the IR receiver cant see the blinking IR transmitter, but only "sees" the sun!
ultra sound -> maybe not so good in rain and wind !
Gps -> expensive! and is it accurate enough? i meen what is best case 2,5 meters ?