📄️ SPI Flash Chips
Eight pin SPI flash chips are a cheap and easy way to add storage to your project. They're available in sizes from 1MB to 128MB, and can be used to store data, firmware, or even a filesystem. They're commonly found on PC motherboards for storing BIOS, FPGAs for storing bitstreams, and even the Bus Pirate for storing the firmware.
📄️ AT24C256 EEPROM
The infamous cheap AT24C256 I2C EEPROM board provides 32K bytes of storage for your projects:
📄️ DS18B20 Temperature
DS18B20 DS18B20
📄️ SI7021, HTU21, SHT21 Humidity & Temperature
SI7021, HTU21 and SHT21 are nearly identical I2C temperature (-10 to 85C) and humidity (0-80%) sensors.
📄️ TSL2561 LUX
TSL2561
📄️ W25Q64 FLASH
A cheap W25Q64 SPI flash board that adds 8 megabytes of storage to your project: