We will be staying at the Citadines St Germain...and I would like to plan ahead for food purchases. I know about the Monoprix and Grande Epicerie at Bon Marche but can anyone tell me other markets. Thanks

There is an outdoor market on Rue de Buci; outdoor stalls as well as proper shops.

Prices at Bon Marche are really high.

There is an organic market on Boulevard Raspail (Tues, Fri, Sunday mornings)

Le Marché St. Germain, a covered market, near the Mabillon métro station might be the closest market, open 6 days a week, closed on Saturday.

I think rue de Buci is one of the highest-priced places in Paris to buy things, also. There is a regular grocery store there in St Germain, after all, a Champion. It's not gourmet nor super-huge (really crowded after work), but it's got the basics. It's probably the closest supermarket to that Citadines. It's at 79 rue de Seine.

la Grande Epicerie is expensive but not to be missed ( even if you just look)
It is the most amazing display of fantastic food.
When in Paris we always go there for a bite.

ttt

The open air market on rue de Seine (not rue de Buci) is no longer, having given way to expensive restaurants and boutiques. However, there is a Carrefour Market (new name for the Champion supermaket) on rue de Seine) that is very reasonably priced. And there's a green grocer almost across the street, at the corner of rue de Buci and rue de Seine.