First, you have to know how many add-ons you want, and what they cost. Next, pledge (or choose manage your pledge) and adjust your pledged amount by however much the add-ons you want cost. Then complete your pledge as normal.
Your end pledge should be the amount of the Tier you selected plus any add-ons. So, if I decided I wanted Route-Breaker at $50, and an add-on for $15, I would pledge $65, and choose the Route-Breaker Tier.
After the campaign concludes, we'll send out a backer survey so you can indicate which add-ons are yours.