Wearing these neck pouches, under a shirt might be okay. However, we use to see a bunch of expats wearing these on the outside while going to and from Angola. Nothing says "tourist" more, except maybe taking a piece of masking tape and writing the word "tourist" on it and placing one on your forehead and one on your back.
Regarding cash, don't tip locals with US small bills. Get some local currency for that. As others have mentioned, currency exchange places usually only deal in $100s, 50s, and 20s. When the new generation of US currency came out, the Angolans referred to it as "Big Heads." They wouldn't accept the older bills and they indeed had smaller pictures of dead presidents.