Just add air? That would be too easy. Apple has packaged all kinds of revised hardware into its thinnest tablet yet:

Fully laminated, 9.7" IPS Multi-Touch LCD with a 2,048 x 1,536 resolution at 264 ppi and antireflective coating

A8X 64-bit CPU (rumored to be a triple-core, 1.5 GHz SoC) paired with 2 GB RAM and M8 motion coprocessor

8-megapixel rear iSight camera capable of recording 1080p/30fps or 720p/120fps video + 1.2-megapixel 720p front-facing camera

Touch ID fingerprint sensor + barometer + dual microphones + 3-axis gyro + accelerometer + ambient light sensor

802.11ac dual-antenna MIMO Wi-Fi + Bluetooth 4.0

16, 64, or 128 GB on-board storage