Your investment in these wet bags goes a long way. Don't think of it as a nappy bag but instead  your parenting all purpose bag.
Designed for use with cloth nappies but its uses go way beyond that - make up bag, swimming bag, 'no leak' sippy cups etc.
 
Small holds 1-2 nappies and is perfect for storing reusable wipes when out and about.
 
Medium double zip bag has two compartments, giving you endless possibilities and holds 4-5 (and often more!) cloth nappies.
 
Large bags will hold about 10-12 nappies - ideal for storing your nappies at home as well as out and about.