Below is a summary of selected additional activities in Pioneer Square district.
1) Mobile Command Centre - D.U.P. base is located in the northern part of the district and there are two jammers nearby - you should destroy them first. Good news is that each of them can be easily destroyed. Bad news is that you'll have to deal with many enemy soldiers with several of them possessing supernatural powers.
Mobile command centre is located in the alley between buildings and the very effective way to destroy its generators and eliminate nearby D.U.P. soldiers is to powerfully hit the ground (Comet Drop for example). Keep repeating this process until you succeed. This is not the only way to do your job here - you can also use distant attacks for example.
2) Blast Shards - Some drones in Pioneer Square district can be found on rooftops, under the highway or on lanterns but you shouldn't have much trouble with them. The only problematic one is located near the bridge between both parts of Seattle. You can get there even if you don't have an access to the southern part of the Seattle yet. Just destroy the barricade and watchtowers (or just bypass them) and then look at one of containers to find the drone.
3) Hidden Camera - The camera you're looking for is located in the place shown on the above screen.
4) Audio Log - You have to reach one of wooden catwalks in marina. The hard disk is located next to the bike (screen above).