Raspberry PI has a dedicated camera port. You can buy camera modules that fully compatible with the PI. There are plenty of example codes and projects on how to use the camera, most of them are opensource.
GPS modules communicates with NMEA standard which has UART for its physical layer. So the easiest way is to connect the GPS to the UART port of the PI. Unfortunately the PI has one UART port (as far as I know) so if you use it for something else (e.g. radio transmitter) it could be a problem. A lot of GPS modules have I2C communication too. In most cases they are not using NMEA messages through I2C, so you have to use a different parser for decode the messages. It is important to check if the I2C line is open by default on the GPS module and what kind of messages are delivered.
Usually the UART port of the GPS module is open by default and you have to configure through some control commands to use the I2C. If this is the case, you have to find a solution to configure the GPS module. UBLOX GPS modules has the feature to load the configuration from an EEPROM, so the GPS can be configured prior flight and the flight computer won't need to make the configuration. But the EEPROM is not built in the actual GPS module, it has to be connected externally.
You can buy ready made boards with UBLOX GPS and EEPROM connected. These modules can be configured via PC with a software provided free by UBLOX. In this way you can configure the GPS to 'arborne' mode and to send messages on I2C lines before you connect to the PI.