Collect the following percentage of total dog tags per chapter on any difficulty level to unlock the corresponding bonus.

Tanker Chapter
Unlimited ammunition bandanna: 46 dog tags (30%)
Stealth apparatus: 76 dog tags (50%)

Plant Chapter
Unlimited ammunition wig: 73 dog tags (30%)
Stealth apparatus: 121 dog tags (50%)
Orange wig (grip gauge will not diminish): 170 dog tags (70%)
Blue wig (Oxygen gauge will not diminish): 218 dog tags (90%)