I agree wityh HRoi, one should buy in Paris what you can't get elsewhere. Plus, it's notoriously the wrong place for hunting out the least bargain... As said (or not) before, I strongly suggest - For bespoke or MTM shoes, the very talented Dimitri Gomez : http://www.dimitribottier.com/1en.aspx
($1650 MTM, $3400 bespoke), but Corthay (http://www.corthay.fr/corthay_en.html
) and Berluti are great too for fine shoes, bespoke or not. And if there's a Mrs Bellison coming with you, check Massaro (2 rue de la Paix, 2nd) for the nicest bespoke women shoes.
For suits, try Cifonelli (31 rue de Marbeuf, 8th ; RTW for $2500 and $5500 bespoke), or Camps de Luca for even more expensive bespoke, but I think this is not appropriate for a weekend only... For shirts, Charvet is the best (28 place VendÃ´me, 1st ; bespoke for $550, MTM for $400, RTW also exists), their ties are top notch too ($170). A little video, in English, presenting Charvet's work : http://www.youtube.com/watch?v=0FPdD255nKM&feature=fvw
Others high-end shirtmakers are Lucca (58 boulevard des Batignolles, 17th) and Courtot (113 rue de Rennes, 6th), who're canvassing and handstitching it all, bespoke, for $250-270. For belts or everything in leather, Duret (29 rue Duret, 16th) makes the most splendid and expensive bespoke stuff : http://www.duret-paris.com/1.aspx
Jacques Ferrand is nearly as good, and cheaper (23 rue des Blancs-Manteaux, 4th). For luxury watches, well... I know nothing about it
Arnys is good for such accessories as yak hair scarfs, cufflinks, and crazy ties/pocket squares : http://www.arnys.fr/shop_arnys/index.php
(ultra expensive, $1150 for that yak scarf, so what?) And for bespoke hats and caps, Guilson (3 rue Saint-Philippe du Roule, 8th) is doing it well. It's a good bespoke tailor as well, but their hats are lovely - the hatmaker's practising since 1960 for the greatest french stars... : http://www.guilson.com/5.aspx
Hope this helps. If you're looking for slightly cheaper things, it's possible too - just ask.