Have you just one night in Bangkok- or do you have a day as well? Which hotel have you booked?
I can't answer re Krabi would have thought Bangkok was your best bet for shopping.
As for trips- I wouldn't book through TC for krabi. You will have plenty options when you get there.

People seem in two minds about Bangkok...some love it (we do)..others hate the hustle and bustle. But there is so much to see and do there thats I think its worth a few days. It also has excellent shopping, both at night and weekend markets and department stores.

Clothes wise, department stores have good quality stuff at reasonable prices and the shopping centres in Bangkok are destinations in themselves. Clothes bought off the markets (t-shirts and the like) are usually pretty good as well (I've still got some from ten years ago going strong) - however these days its just as cheap to buy such clothing in the UK. Otherwise you can get something tailormade at a tailors - best to rely upon recommendations for this.

In Krabi a lot of the trips out are by boat...rent a long-tail boat, about twenty pounds for the day with skipper. These are ok for trips to nearby beaches and islands providing the seas not to rough. You can pick thses up at the beach in Ao Nang. Long-tails also run a regular service from Ao Nang to nearby Railley beach. We usually hire a taxi for the day for our land based trips. Tiger Cave temple is worth a visit if your fit - over 1200 steep steps to shrine at top of hill with great views over Krabi town and Phang-nga bay. Its a while since I've been into Krabi Town itself as this is a working town with just a few small department stores - at least when we stayed there at the Krabi Meritime.

We have booked Bel Aire Princess hotel in Bangkok I think? We are there for an evening, and then the most part of the next day. Arrive at approx 15:00 on the 17th, and depart around 18:00 on the 18th.

So realistically we are looking for a nice restaurant on the 17th, and then a good couple of bars for a few drinks, and then a browse round the city and the shops etc on the 18th.

Any tips on places, and where is worth visiting would be appreciated.

If you want to eat nearby try Lemongrass, 2 stops away on the skytrain.Reception will point you in the right direction. Other members will have their own recommendations as well. You may like the BedSupper Club- the place to go but we gave it a miss as I didn't fancy the bit about 3 sittings in an evening. Just up from your hotel is Gullivers- a great bar and a barn of a place.
A must do for the following day is the Grand Palace. Take the skytrain to the terminal(Saphan Taksin) and take the tourist boat. That way you will have commentary along the way too. On return take the skytrain to Siam and your pick of places to shop