Info about local conditions, shops etc.
Makerspaces
KTH's Electronics Hobby Lab - ELAB - is a 5 minute walk away. Decently equipped with electronics engineering tools and workbenches, as well as a ton of components is available for purchase (all the basic passives, wires, protoboards, some arduino modules etc). You may politely ask to be let in (despite normally being members only). Contact Marek Baczynski (es.htk|abkeram#es.htk|abkeram or twitter DM @markshouts) to arrange an entry.
Electronics/Hardware shops
The largest and potentially most well-stocked chain of stores for electronics and hardware in Stockholm is Kjell & Company. They have several stores in relatively close proximity to KTH (~1km), though no outlet on campus. They are open until 5/6pm on Saturday, but do not open until 11am on Sunday.