The possibilities are only limited to how creative your mind is. There are pleanty of Generic ones for lack of a better term patient/nurse, patient/doctor cop/prisoner handyman/ horny house wife, Naughty school girl/teacher or Principal could go on and one as this has to be one of if not our favorite activities.
Sure costumes and sex lingerie are always good to add to the excitement but you can always improvise. I'll give you and example. The other day I was repairing our dishwasher (for real not fantasy involved) So I have my toolbox and parts spread all over the place and after about 2 hours or so I get the thing fired up just as I'm ready to call to my wife and tell her no more dishpan hands for her I hear something behind me and I turn to see my wife wearing a very sexy Teddie see through of course with a long sheer robe and she's got the thigh high stockings on and the heels etc. hair all done up. I'm like duh! She says I really appreciate you repairing y dishwasher sir but my husband didn't leave me the check book so I don't know how I'm going to pay you. I quickly played along and said oh I take credit cards Visa, MasterCard American express mam. She said oh sorry I don't have any of those either and she took my hand and said we'll just have to work something out. So off to the bedroom she leads me and lets say I got a Great tip along with more then ample compensation for my services..........
I laughed and said so this is how you take care of the bills when I'm not around huh. and we both laughed yup every single one of them.........lol
So you see sometimes you can just improvise and wing it. Take any situation and just play with it in your mind you dont necessisarily have to play it out like a script or even tell her about it. If you think your wife will be eager to play along and improvise you just might surprise yourself on how much fun you'll have. To be honest one of the best places to find inspiration are those cheesy porn movies. You know where the only thing worse then the "acting" is the totally ridiculous plot or lack there of.
You'll definitely have fun no matter what role (s) you pick.