what about more 'sciency' toys/equipment
eg
microscope
telescope
binoculars
ladybirds/butterflies/stick insects kit
stethoscope
fossils (real or play kit)
metal detector
or sports/ outdoor things
bike
scooter
roller skates
mini skateboard
soft bow & arrows
tent
compass
head torch
basket ball net
if you have a lot of construction toys already perhaps you don't need more?
I am not sure about the value of an 'experience' present for a 4/5 year old - I think on the day he may feel very sad if he hasn't got an exciting thing to open.