Arduino Uno Multiple Modules
Let's see which device uses which communication protocol:


WiFi Module (ESP8266 ESP-01) uses Serial communication.
RTC (Real Time Clock - DS1307) uses I²C communication.
RFID Reader (RC522) uses SPI communication.
SD Card Module also uses SPI communication.


Now, the Arduino UNO supports One I²C, One SPI and One Serial (by default) communication port. 

So, you can easily connect your Wifi and RTC modules.

Now, actual problem is: "How to access multiple SPI interfaces on Arduino" (and that is a solved problem).

Hope it helps and you don't have to buy an Arduino MEGA.