digital ear thermometer is very quick to take temp - although was told by NHS direct late one night when i had a feverish baby that they can be a bit unreliable in small babies so you may want to look if there is anything else better suited to tinies (it's something to do with not being able to get probe far enough into their ear canal which made sense to me given some of the wildly differing readings i get with it).
saline drops definitely.
calpol from 2months, nurofen from 3mths. calpol better for fevers, nurofen better for things like teething, so definitely worth having both available. both have different dosing regimes so be careful you know which is which when using.
make sure you get a syringe for dispensing these - much the easiest way to get meds into a baby.
nappy rash stuff is good - metanium or bepanthen. as with other things, you don't want to have to think about buying it when your baby has a very sore bottom!
calamine might be a good idea for heat rash or anything else generally itchy. you can get a mix of calamine/aqueous cream which i have - although only had to use it on myself!
not strictly first aid, but i've found dentinox cradle cap shampoo really good for cradle cap (and less smelly than aqueous cream)
then things like cotton wool balls, cotton buds, tissues, tweezers are always good to have available.