I also tip 1.-2 per bag, min. 5.00. But, here is a little tip. Look at what they put on your bags for routing. If it says, for example: BDL/MCO that means it is going to be sorted by someone and hopefully put on the correct plane. Remember the skycaps take the bags to the conveyer belt used (in most cases) by the airline counter reps. It usually does not go anywhere special(some airports do have special conveyers for skycaps). It is at the other end that it gets botched up (if it is going to). You can do your part by watching what they put on the bags at the get go.