Typically the
must see sights of Paris take 3 to 4 full days. Availability of only 2 partial days means compromise and only you really know what you want to see and what you will be willing to overlook. I recommend a good guide book.
I don´t really think that there is a mall worth visiting anywhere on the globe but maybe the best Paris has to offer is the
Forum des Halls in the 1st arrondissement. There are
cheap places to eat all over Paris, none of which I might specifically recommend.
Paris has no Oyster card such as what one finds in London. The travel solutions are varied and depend greatly upon when you arrive and depart and how. You might consider a booklet of 10 tickets t+ which are valid on the bus, métro, tramway, or funicular. Cost is 14.90€ vs. the t+ individual cost of 1.90€. Tickets are sold at any train or métro station kiosk.
There are a number of SIM cards sold. More expensive cards are available by Orange, Bouygues, SFR, and FREE at their respective retail boutiques. Inexpensive options are Lebara or Lycamobile which sell cards at tabacs and magazine stores for as little as 10€. Recharging any of these on line with a non-French credit card will be highly problematic.