JR Gear's Ultra light dry bag with TPU clear window makes for locating stuff in seconds.
The magnetic closure has a better seal at the opening than traditional closure. Extremely light weight but durable enough.

Features
30D Cordura with silicon coating to increase the strength and durability
PU backing
Ultra light
Magnetic closure
Taped seam for waterproofing
IPX4

Specifications:

2.5 Ltr 15 x 30 cm
5 Ltr 18 x 38 cm
10 Ltr 20 x 48 cm
15 Ltr 23 x 53 cm
20 Ltr 25 x 58 cm
30 Ltr 28 x 66 cm
40 Ltr 30 x 74 cm

NOTE: Bag in photo is indicative of colour only - not the actual size