Also free food at any Leon restaurant this Saturday! From their newsletter:
We know how important it is to eat well. Especially the day before you race. This Saturday 25th April we'll be giving all London Marathon runners a free Meatball or Gobi lunchbox to help you get your bodies ready for the big day. Simply show your printed race number to our team and we'll look after you.
And Meat liquor / Meat mission:
Show your medal for completing the London Marathon 2015 or show your badge if you're an official volunteer to get a free burger (usually £8ish) on Sun 26 Apr (the day of the race) from any London branch of the Meat Liquor burger joint chain. These are: Meat Liquor (Marylebone), Meat Market (Covent Garden), Meat Mission (Hoxton) or Chicken Liquor (Brixton).
And Chipotle is doing BOGOF:
Running the London Marathon this year? Bring your racing bib to any London Chipotle on Sunday, 26th April and we'll treat you to a buy-one/get-one burritos, bowls, salads or tacos!
The interface is a little buggy (you have to click through to each runner to favourite them - if you tap the star from the search results it doesn't add them to the list) and my GPS location is on the wrong side of the river, but I live in hope it'll help on the day.
I'm also a 34B and I've tried a lot of different brands. My personal favourites are the Moving Comfort bras, specifically the Phoebe model - I've got two of those and have run a marathon in each with only one small patch of chafing at the centre back (which was absolutely fine on my 20 milers go figure).