Well, you can only select one reward. But no worries - there is always a solution!!
If you want to select multiple rewards,
1) Choose what you like.
2) Then, sum up the amount of each reward.
3) Make your pledge using the option of "make your pledge without a reward."
4) Enter the total amount you calculated (see the step 2)
5) Drop me a note on which rewards you would like to receive. Either you can leave the message on Kickstarter or email@example.com. Don't forget to leave your total amount so that I know the details is for whom.
6) Once everything goes through and confirm the information, you will receive a message directly from me either via Kickstarter or an email (depending on which channel you used in step 5).
Still not clear? Just contact me with your questions!