The GPS is very useful and handy. Don't assume you have to buy a very expensive GPS to get the job done, either. I bought a Garmin eTrex for about $120 in 2006 for a wilderness DIY elk hunt. Such a simple GPS can do a number of things for you: (1) inform you of the sunrise/sunset time at your exact location, (2) inform you of the altitude of your location, (3) set a way point which you can later select to navigate to -- for example, set a way point on your camp before leaving it in the morning and select to navigate to it on your way back home, and the GPS will give you a pointer in the direction of your camp and an indication of how far (10 miles, 1 mile, 400 feet). This can be particularly useful when it gets dark -- for example returning to camp after boning out your downed elk that you shot in the last minutes of shooting light. The GPS gives you some confidence that you wouldn't otherwise have, I think, to get after it and focus on your hunting.
Of course, you want a back-up in case the GPS fails -- map and compass. Additionally, the GPS may not work well under forest canopy or under very heavy clouds/precipitation. There is no substitute for the benefits of remaining generally oriented to your landscape (my truck is downhill, on the road, if I walk downhill -- on the correct side of the ridge -- I have to hit the road and hence my truck is either up or down the road from where I intersect the road).
Additionally, the GPS can be very handy in marking a kill site or a water hole you want to return to later.
When it comes to scent, there are basically two types; those that attract and those that mask. I've tried both on many occasions. There are lots and lots of "doe in heat" scents, designed to attract a big buck into range. I've also used a "cow in heat" scent while elk hunting.
Another scent would almost be better named as a "coverup smell". The main goal is to cover up human odor or mask it. Though I don't believe you can ever totally eliminate all human...