Well nowadays i only take a larger handbag for short trips (say max 3hrs) and take for bubs the following:

2 nappies
travelcase wipes
2 or 3 bibs (reflux baby so CONSTANT,constant vomiting)
nappy sacks (whole pack)
small toy
spare dummy
bottle water or milk depending on feed times

If i go out all day or out for the evening to friends place then i take the big nappy bag including all the above and the following;
2 sets of spare clothes
another 2 nappies
Bottle of water
Milk Bottles
Homemade Dinner (or lunch)
numerous bibs
burping clothes (actually are cloth nappies)
a few blankets,wraps if going for a nap at someones place

IT'S RIDICULOUS!!