Bonn's compact old town makes for pleasant shopping on foot, with the Marktplatz as the natural starting point.
The Marktplatz hosts a daily fruit and vegetable market (closed Sundays) surrounded by small boutiques and cafes. The baroque Altes Rathaus anchors the square. Open-air stalls rotate seasonally, and prices are reasonable for a German city.
Kaiserpassage Mall in Bad Godesberg opened in 2009 and has the usual mix of international brands (Esprit, H&M) and local boutiques. Skylights keep it bright during the day, and you can see Poppelsdorfer Schloss from inside.
For something more atmospheric, the Siegburg Munsterplatz (Cathedral Square) is a 15-minute ride northeast. The pottery here makes a distinctive souvenir. The annual Weihnachtsmarkt (Christmas Market) transforms the square in late November and December with handcrafted decorations, baked goods, and warm Gluhwein.