Most exams: eat as normal
Brain, spine and joint MRI do not require an empty stomach. Eat and drink so you are comfortable lying still. Skip heavy caffeine if you are anxious. It can make a closed scanner feel harder.
When fasting is requested
Some abdominal and MRCP (bile duct) protocols ask for several hours without food. A pelvic study may ask for a partly full bladder. Follow the message from your clinic. A general rule from the internet is how people arrive unprepared.
Medicines
Blood pressure tablets, thyroid tablets and most other daily medicines should be taken with a sip of water unless you were told not to. Insulin and other diabetes treatment may need a plan if you are fasting. Pain patches and nicotine patches are sometimes removed because of metal or heating. Mention them.
If you were given a sedative to collect before a claustrophobic scan, you need someone who can take you home. Do not drive after it.