I'd like to travel on a 303 again. Unfortunetly, only one is in preservation now, I beleive, and that's at the non-electrified Bo'ness railway.
They used to operate on my local line, and I was able to use them often (but I always prefered the 314s). Looking back, I do wish I could travel on one again. I'm fortunate enough to still use the 314s on an (almost) daily basis, so there's that at least.
Even in Hornby modelled one (preferablly both) of these classes, that'd please me!
Also, something I'dl ike to do again that's far from impossible, but very likely, is travel behind the power of a steam locomotive. I've only ever done it on the Isle of Wight Steam Railway and once at the Bo'ness Railway, but a railtour behind an A4 (preferablly Mallard, but that's not going to happen!) would be the most awesome thing ever.
Oh, and travel on a 221. Done it once from Motherwell - Glasgow Central. Loved it and would like to do a longer journey on one!