Groupon for Windows Phone just got itself a big update, to v4.0, with the facility to 'buy' multiple offers at once. Some details and links below. Note that the old Nokia-published version from 2011/2012 can be ignored/removed now - this is a complete first party replacement.

From the Store description, we get the changelog over and above v3.x:

What's new for Version 4.0: 

• Groupon now allows you to add goods to your cart and continue shopping!
• You can search for deals from anywhere in our app!
• Find nearby deals easily with the nearby tab!

Some stock screens of Groupon in action (I tried to get the 'search for deals from anywhere' working and failed...!), showing typical offer fare and (right) showing the new 'add to cart' system:

Maybe it's me. It seems that you're either a Groupon customer or you're not. In the UK at least, every single thing I browsed through in the system was something I didn't need - yoga classes, cutlery sets, human resource classes, etc. A bit like those Sunday magazine gadget supplements, full of hundreds of things you didn't think you needed until you saw them on the page! And items may be "60% off", but you still have to buy them using the other 40% from your already strained wallet...

Having said that, if you're after something specific then there's a good search system - I noted a wedding party for 60 at a castle with a saving of £6000, for example!

Comments welcome. You can download Groupon for free (obviously) here in the Store.