First piece of advice: Don't underestimate the task. Pen-y-Fan may not be the biggest mountain, and people may stroll around on its slopes like it's a park, but people who underestimate mountains and the weather end up as statistics.
I would suggest the equipment you need includes:
- Someone who knows what they are doing, since you describe yourself as a complete novice.
- Walking boots and socks. Not trainers, nor workboots. Wear your boots in before you go.
- Walking trousers. Not jeans, they are terrible when they get wet.
- Layered tops, so you can adjust as you go along.
- Waterproofs. Tops & bottoms. Even if it starts out as a nice day.
- A hat. For protection from the sun, rain, cold... whatever the weather throws at you.
- A "day bag" i.e. small rucksack, but make sure it's big enough. One that takes a bladder for water would be good.
- Water. Take more than you think you will ever need.
- Food. Fruit, dried fruit, nuts & seeds are good as well as the usual sandwiches etc.
- Map and compass. And make sure you know how to use them and know your route before you go. I was on Pen-y-Fan once in snowy conditions when fog descended. Boy was I grateful for orienteering experience.
- First aid kit, particularly stuff for your feet.
- Space blankets. They are fantastic for retaining body heat.
- Phone
- Camera. To record the proud moment when you place another rock on the cairn at the summit.
You'll be spending a few bob at the outdoors store, but if you are properly prepared you will be able to enjoy the experience and your achievement.
And don't be afraid to postpone the attempt if you find it too tough or if the weather turns. Better to go back another day than to get into trouble.
Good luck!
