SIM Cards and Money Exchange
If you did not get your SIM card in Jeddah, Makkah has many mobile carrier and phone shops where SIM cards are available. The Clock Tower as well as most shopping areas will have shops by their relevant mobile carrier company. There are several companies such as Zain, Mobily and STC, but instead of getting hung up on which company to go with it can be good to look at what data deals they have offered as it's typically cheaper to use data to call home via a smartphone app.
For a SIM card, you will need to show your visa and passport. There will be codes to check your balance and instructions on how to top-up, make sure you understand these clearly or have some written support given to you.
For the cash you have with you, it is best to get that exchanged. Shop around, as different money exchange shops have different rates. Sometimes you may get a slightly better rate if you ask.
If you lose or run out of money there are ATMs around Masjid al-Haram, certain cards are supported so you will have to see if you can withdraw cash there.
You can search Google Maps for ATMs in Masjid al-Haram.