It depends. You can only buy boosters that are available to you, based on your level progress. For example, the knife booster doesn’t become available until after you’ve reached level 14. Once it becomes available, you are able to buy it.

To purchase a boost, click on the (i) icon near “Select Boosts” on the Level Card (See above image) or click on the “Store” button. You will be given  information about each boost, in addition to being able to buy it.