Riga as your base, and the day trips that add up
Most trips to Latvia are Riga plus a handful of day trips, and those outings decide the pack more than the city does. Jūrmala is a short train ride to the beach. Sigulda and Cēsis sit on the railway into the Gauja valley. Rundāle Palace is a drive south towards Bauska, and Kuldīga, with its wide waterfall and old town, is a longer day out to the west. Each one means routes, timetables and photos away from the hotel Wi-Fi.
Three or four days in Riga with one outing fit in 3 GB, valid for 15 days. A week with three or four of those trips is where the 5 GB pack, valid for 30 days, earns its place. If you hire a car and loop the Kurzeme coast to Ventspils and Liepāja, navigation runs all day and 10 GB is the comfortable size. Not sure? The calculator sizes it from how you use your phone.