Merlin, in tha vast majority of cases, gifts, aren't really appreciated all that much. Money is what these people need, and a slightly more generous tip will mean the most to them. There are exceptions, I have a multi-year relationship with a fine tracker in Namibia, to whom I brought my old binioculars when I upgraded this past year. I knew what he was using, and knew these would be cherished (and I checked with the PH to make sure it was a good idea as well.) My spouse developed a relationship with the housekeeper of our bungalow, a tiny little woman in her fifties - who looked seventy-five, and gave her the fleece jacket she had brought along. It too was much appreciated. But these were in addition to a generous tip.
The SCI bags are a good idea if you are going to a primitive area, and if you have had good advice about what to include. However, much Namibian hunting is done in ranch country, and the schools there are pretty modern by African standards. Ranch country also has nice stores in the small towns, well stocked with SA, Euro, and American products. Again, what the staff needs is money to spend in them. I am sure many will take exception to this, but I have found the whole blue bag thing seems to be focused a little too much on the giver than the recipients. That said, if you are planning to spend two weeks in the Caprivi, then you will find very different conditions there where material aid might be more welcome.
Finally, I would work with your PH on how to handle the tips. The vast majority of these folks are very honest in apportioning tips to the staff so that all benefit - to include those with whom you have little or no contact. As noted above, I prefer to tip my tracker seperately and I have never had a PH object to that preference.
There are several PHs and outfitters who are members here, and I am certain they will offer advice from their perspective as well.