When activities are placed on the arrows, there can be a greater sense of the concurrent nature of various processes and tasks as the arcs move forward towards project completion; activity-on-node setups emphasize the greater codependence of certain processes and tasks by making movement from nodes impossible until all required activities have been completed (NetMBA 2011). All projects could technically be mapped out as either activity-on-arc/arrow or activity-on-node charts, with project appropriateness and project manager preference being the determining factors (NetMBA 2011). Gantt charts can be seen as solely activity-on-node charts, though they aren't typically described as such and are not really directly comparable in a meaningful way with the other chart types in this regard. Making a...

The retrieval of ingredients from the fridge and breadbox, taking out of the utensils, removal of the bread, spreading of the ingredients, resealing of al packages, slapping the bread together, and putting everything way would all be parts of the process. The critical path sequence would follow basically this same order, with the need for ingredient removal clearly coming before the need to put everything away, and the sandwich making process in between.
References

MindTools. (2011). Gantt Chart. Accessed 13 October 2011. http://www.mindtools.com/pages/article/newPPM_03.htm

NetMBA. (2011). PERT Chart. Accessed 13 October 2011. http://www.netmba.com/operations/project/pert/