Yes. You can use external memories with I2C, SPI or parallel interface to the PSoC. PSoC has the I2C and SPIM user modules using which serial memories may be accessed. Also, parallel memories can be accessed by generating the necessary Address, Data and Control signals using the GPIO. The following example project demonstrates how to interface a PSoC to an I2C EEPROM.
Interfacing an I2C EEPROM
Also, using the EEPROM user module a part of the internal Flash may be used to store configuration data