Prices on the low-cost airlines will increase dramatically if you wait until last-minute to book. Try pricing out your trip with Easyjet.com and Ryanair.com as if you’re leaving today and you will get a good idea of their last-minute pricing.

Also, Ryanair charge 40(?) Euros if you check in at the airport. Check in ahead of time online and print your boarding pass for only 5 Euros.

Ryanair CIA-GRO booked today for travel today is 208 Euros + fees. BTW, these airports aren’t so bad; CIA is actually closer to Rome proper than FCO, and GRO is a nice little airport with good bus connections to Barcelona and the region.

VCE-FCO booked today for travel today would be 99 Euros + 11 Euros for 1 20kg bag. (BTW, Alitalia about the same price for last minute currently).
BCN-CDG today would be 160 Euros + bag.

Indeed book it now, unless you expect the chance that you will cancel is > 50% !

Cool, I’ll definitely start booking those this week.
I’m assuming train fares are the same as well?
Oh, how strict are the airlines about their carry on policy? I will be traveling with a triathlon backpack. The length and width are within the requirements, but tue depth is about 3 inches too deep. My bag will not be stuffed to capacity, so I figured I could just smash it down some or tie rope around it to condense it.

I had no troubles with carrying on a slightly oversized backpack. I flew Ryanair, easyjet, vueling, smartwings, and spanair. None of these were strict. Definitely only bring one piece of carry on, and as long as it will fit in the overhead, you should have no problem. Definitely book as soon as possible as well.

Train fares usually don’t fluctuate quite so dramatically, but high-demand international train routes on busy days can be expensive if you book last minute and only the most flexible (refundable) seats in first class are available—or something like that.

For example, a Ryanair fare at 5 Euros+fees bought well in advance that becomes 200 Euros+fees last-minute represents a 40x increase. Whereas a 29 Euro train fare bought well in advance might be 129 Euros on a long-ish crossborder route last minute — of course not precise, but just so you get the gist of it.

In my experience, generally the bag requirements are strict. I think it depends on who is working when you actually check your bag in, but Ryanair does have a reputation for being strict with dimensions and weight. They make a lot of money from baggage fees (gotta pay for those 5 Euro fare sales somehow, I guess!) . If it’s able to be easily compressed into the bag sizer, then you should be fine. For checked bags, be careful with excessive ropes or straps or ties — they can snag in the conveyor belts.

Are the size restrictions for carry on comparable to Southwest Airlines here in the US?
Carry on for the trains should be about the same correct?

Not sure off the top, but I believe Ryanair and Easyjet have their carry-on dimensions posted on their websites. You’d think Ryanair would have similar limits as Southwest, since Ryanair modeled itself on Southwest and both airlines fly only Boeing 737s. However, my hunch is Ryanair is not nearly as generous.

Trains are usually better with carrying on your backpack n’ stuff. There is usually room above your seats for some luggage… the big backpacks will not always fit, but there are some luggage racks right when you get on the train where you can store your over sized luggage.